Revert "[Vim/YCM] Fix missing system headers when YCM was built with its own libclang."

This reverts commit 75a861f2.

Reason for revert: It turns out this is an upstream issue. See:

- https://chromium-review.googlesource.com/c/chromium/src/+/1482557
- https://github.com/Valloric/ycmd/pull/1193

Original change's description:
> [Vim/YCM] Fix missing system headers when YCM was built with its own libclang.
> 
> Bug: 932667
> Change-Id: I2eb9965da1eb3f9ad4a5ce103cf6e32d35019e48
> Reviewed-on: https://chromium-review.googlesource.com/c/1476105
> Auto-Submit: Sidney San Martín <sdy@chromium.org>
> Commit-Queue: Sidney San Martín <sdy@chromium.org>
> Commit-Queue: Asanka Herath <asanka@chromium.org>
> Reviewed-by: Asanka Herath <asanka@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#632846}

TBR=sdy@chromium.org,asanka@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 932667
Change-Id: I5a684c91723d28470e1d903cd74674ce145b421b
Reviewed-on: https://chromium-review.googlesource.com/c/1483709Reviewed-by: Sidney San Martín <sdy@chromium.org>
Commit-Queue: Sidney San Martín <sdy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#634829}

tools/vim/chromium.ycm_extra_conf.py

@@ -296,13 +296,6 @@ def GetClangOptionsFromNinjaForFilename(chrome_root, filename):
   # Chromium's includes are relative to that.
   additional_flags = ['-I' + os.path.join(chrome_root)]
 
-  # Fix missing system headers. For details, see
-  # <https://github.com/Valloric/YouCompleteMe/issues/303>
-  clang_root = os.path.join(
-    chrome_root, 'third_party/llvm-build/Release+Asserts')
-  additional_flags += ['-isystem', os.path.join(clang_root, 'include')]
-  additional_flags += ['-isystem', os.path.join(clang_root, 'include/c++/v1')]
-
   # Version of Clang used to compile Chromium can be newer then version of
   # libclang that YCM uses for completion. So it's possible that YCM's libclang
   # doesn't know about some used warning options, which causes compilation

tools/vim/tests/chromium.ycm_extra_conf_unittest.py

@@ -20,12 +20,6 @@ import sys
 import tempfile
 import unittest
 
-_common_flags = [
-  '-I[SRC]',
-  '-isystem', '[SRC]/third_party/llvm-build/Release+Asserts/include',
-  '-isystem', '[SRC]/third_party/llvm-build/Release+Asserts/include/c++/v1',
-  '-Wno-unknown-warning-option'
-]
 
 def CreateFile(path, copy_from=None, format_with=None, make_executable=False):
   """Creates a file.
@@ -169,8 +163,9 @@ class Chromium_ycmExtraConfTest(unittest.TestCase):
         self.ycm_extra_conf.GetClangOptionsFromNinjaForFilename(
             self.chrome_root, os.path.join(self.chrome_root, 'one.cpp'))
     self.assertEquals(
-        self.NormalizeStringsInList(clang_options), _common_flags + [
-            '-I[OUT]/a', '-I[OUT]/tag-one'
+        self.NormalizeStringsInList(clang_options), [
+            '-I[SRC]', '-Wno-unknown-warning-option', '-I[OUT]/a',
+            '-I[OUT]/tag-one'
         ])
 
   def testOutDirNames(self):
@@ -195,9 +190,8 @@ class Chromium_ycmExtraConfTest(unittest.TestCase):
     self.assertTrue('flags' in result)
     self.assertEquals(
         self.NormalizeStringsInList(result['flags']), [
-            '-DUSE_CLANG_COMPLETER', '-std=c++14', '-x', 'c++'
-        ] + _common_flags + [
-            '-I[OUT]/a', '-I[OUT]/tag-one'
+            '-DUSE_CLANG_COMPLETER', '-std=c++14', '-x', 'c++', '-I[SRC]',
+            '-Wno-unknown-warning-option', '-I[OUT]/a', '-I[OUT]/tag-one'
         ])
 
   def testGetFlagsForFileForUnknownCppFile(self):
@@ -209,9 +203,8 @@ class Chromium_ycmExtraConfTest(unittest.TestCase):
     self.assertTrue('flags' in result)
     self.assertEquals(
         self.NormalizeStringsInList(result['flags']), [
-            '-DUSE_CLANG_COMPLETER', '-std=c++14', '-x', 'c++'
-        ] + _common_flags + [
-            '-I[OUT]/a', '-I[OUT]/tag-default'
+            '-DUSE_CLANG_COMPLETER', '-std=c++14', '-x', 'c++', '-I[SRC]',
+            '-Wno-unknown-warning-option', '-I[OUT]/a', '-I[OUT]/tag-default'
         ])
 
   def testGetFlagsForFileForUnknownCppNotTestFile(self):
@@ -223,9 +216,8 @@ class Chromium_ycmExtraConfTest(unittest.TestCase):
     self.assertTrue('flags' in result)
     self.assertEquals(
         self.NormalizeStringsInList(result['flags']), [
-            '-DUSE_CLANG_COMPLETER', '-std=c++14', '-x', 'c++'
-        ] + _common_flags + [
-            '-I[OUT]/a', '-I[OUT]/tag-default'
+            '-DUSE_CLANG_COMPLETER', '-std=c++14', '-x', 'c++', '-I[SRC]',
+            '-Wno-unknown-warning-option', '-I[OUT]/a', '-I[OUT]/tag-default'
         ])
 
   testGetFlagsForFileForKnownObjcFile = TestLanguage('eight.m', 'objective-c')
@@ -249,9 +241,8 @@ class Chromium_ycmExtraConfTest(unittest.TestCase):
     self.assertTrue('flags' in result)
     self.assertEquals(
         self.NormalizeStringsInList(result['flags']), [
-            '-DUSE_CLANG_COMPLETER', '-std=c++14', '-x', 'c++'
-        ] + _common_flags + [
-            '-I[OUT]/a', '-I[OUT]/tag-default'
+            '-DUSE_CLANG_COMPLETER', '-std=c++14', '-x', 'c++', '-I[SRC]',
+            '-Wno-unknown-warning-option', '-I[OUT]/a', '-I[OUT]/tag-default'
         ])
 
   def testGetFlagsForFileForUnknownUnittestFile(self):
@@ -263,9 +254,9 @@ class Chromium_ycmExtraConfTest(unittest.TestCase):
     self.assertTrue('flags' in result)
     self.assertEquals(
         self.NormalizeStringsInList(result['flags']), [
-            '-DUSE_CLANG_COMPLETER', '-std=c++14', '-x', 'c++'
-        ] + _common_flags + [
-            '-I[OUT]/a', '-I[OUT]/tag-default-test'
+            '-DUSE_CLANG_COMPLETER', '-std=c++14', '-x', 'c++', '-I[SRC]',
+            '-Wno-unknown-warning-option', '-I[OUT]/a',
+            '-I[OUT]/tag-default-test'
         ])
 
   def testGetFlagsForFileForUnknownBrowsertestFile2(self):
@@ -277,9 +268,9 @@ class Chromium_ycmExtraConfTest(unittest.TestCase):
     self.assertTrue('flags' in result)
     self.assertEquals(
         self.NormalizeStringsInList(result['flags']), [
-            '-DUSE_CLANG_COMPLETER', '-std=c++14', '-x', 'c++'
-        ] + _common_flags + [
-            '-I[OUT]/a', '-I[OUT]/tag-default-test'
+            '-DUSE_CLANG_COMPLETER', '-std=c++14', '-x', 'c++', '-I[SRC]',
+            '-Wno-unknown-warning-option', '-I[OUT]/a',
+            '-I[OUT]/tag-default-test'
         ])
 
   def testGetFlagsForFileForKnownHeaderFileWithAssociatedCppFile(self):
@@ -291,9 +282,8 @@ class Chromium_ycmExtraConfTest(unittest.TestCase):
     self.assertTrue('flags' in result)
     self.assertEquals(
         self.NormalizeStringsInList(result['flags']), [
-            '-DUSE_CLANG_COMPLETER', '-std=c++14', '-x', 'c++'
-        ] + _common_flags + [
-            '-I[OUT]/a', '-I[OUT]/tag-three'
+            '-DUSE_CLANG_COMPLETER', '-std=c++14', '-x', 'c++', '-I[SRC]',
+            '-Wno-unknown-warning-option', '-I[OUT]/a', '-I[OUT]/tag-three'
         ])
 
   def testSourceFileWithNonClangOutputs(self):
@@ -319,9 +309,8 @@ class Chromium_ycmExtraConfTest(unittest.TestCase):
     self.assertTrue('flags' in result)
     self.assertEquals(
         self.NormalizeStringsInList(result['flags']), [
-            '-DUSE_CLANG_COMPLETER', '-std=c++14', '-x', 'c++'
-        ] + _common_flags + [
-            '-I[OUT]/a', '-I[OUT]/tag-four'
+            '-DUSE_CLANG_COMPLETER', '-std=c++14', '-x', 'c++', '-I[SRC]',
+            '-Wno-unknown-warning-option', '-I[OUT]/a', '-I[OUT]/tag-four'
         ])
 
   def testSourceFileWithOnlyNonClangOutputs(self):
@@ -333,9 +322,8 @@ class Chromium_ycmExtraConfTest(unittest.TestCase):
     self.assertTrue('flags' in result)
     self.assertEquals(
         self.NormalizeStringsInList(result['flags']), [
-            '-DUSE_CLANG_COMPLETER', '-std=c++14', '-x', 'c++'
-        ] + _common_flags + [
-            '-I[OUT]/a', '-I[OUT]/tag-default'
+            '-DUSE_CLANG_COMPLETER', '-std=c++14', '-x', 'c++', '-I[SRC]',
+            '-Wno-unknown-warning-option', '-I[OUT]/a', '-I[OUT]/tag-default'
         ])
 
   def testGetFlagsForSysrootAbsPath(self):
@@ -351,7 +339,8 @@ class Chromium_ycmExtraConfTest(unittest.TestCase):
             '-std=c++14',
             '-x',
             'c++',
-        ] + _common_flags + [
+            '-I[SRC]',
+            '-Wno-unknown-warning-option',
             '-I[OUT]/a',
             '--sysroot=/usr/lib/sysroot-image',
             '-isysroot',
@@ -371,7 +360,8 @@ class Chromium_ycmExtraConfTest(unittest.TestCase):
             '-std=c++14',
             '-x',
             'c++',
-        ] + _common_flags + [
+            '-I[SRC]',
+            '-Wno-unknown-warning-option',
             '-I[OUT]/a',
             '--sysroot=[SRC]/build/sysroot-image',
             '-isysroot',
@@ -389,7 +379,8 @@ class Chromium_ycmExtraConfTest(unittest.TestCase):
             '-std=c++14',
             '-x',
             'c++',
-        ] + _common_flags + [
+            '-I[SRC]',
+            '-Wno-unknown-warning-option',
             '-I[OUT]/b',
             '-isystem[OUT]/a',
             '-isystem', '[SRC]/build/c',
@@ -407,7 +398,8 @@ class Chromium_ycmExtraConfTest(unittest.TestCase):
             '-std=c++14',
             '-x',
             'c++',
-        ] + _common_flags + [
+            '-I[SRC]',
+            '-Wno-unknown-warning-option',
             '-I', '[OUT]/a',
             '-I', '[OUT]/tag-eleven'
         ])