Revert "Pull libunwind, libcxx, libcxxabi from a different mirror."

This reverts commit edbc09da.

Reason for revert: broke bot_update on internal bots
https://ci.chromium.org/p/chrome/builders/ci/linux-chromeos-chrome
https://ci.chromium.org/p/chrome/builders/ci/linux-chromeos-chrome/3328

Original change's description:
> Pull libunwind, libcxx, libcxxabi from a different mirror.
> 
> The current mirror has been stale since LLVM moved to github.
> 
> This checks out the same revisions as previously, so this should
> be a no-op.
> 
> Bug: 1048253
> Change-Id: I589991a315c2ea178dc4c2dde834943d1afd9bcd
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2062879
> Commit-Queue: Nico Weber <thakis@chromium.org>
> Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
> Auto-Submit: Nico Weber <thakis@chromium.org>
> Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#742720}

TBR=thakis@chromium.org,thomasanderson@chromium.org

Change-Id: I0db1d8eddbf5531dc547d6375576a5c6b2ac2976
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1048253
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2064812Reviewed-by: Ben Pastene <bpastene@chromium.org>
Commit-Queue: Ben Pastene <bpastene@chromium.org>
Cr-Commit-Position: refs/heads/master@{#742739}

DEPS

@@ -334,9 +334,9 @@ vars = {
   # Also, if you change these, update buildtools/DEPS too. Also update the
   # libc++ svn_revision in //buildtools/deps_revisions.gni.
   'clang_format_revision': '96636aa0e9f047f17447f2d45a094d0b59ed7917',
-  'libcxx_revision': 'd9040c75cfea5928c804ab7c235fed06a63f743a',
-  'libcxxabi_revision': '196ba1aaa8ac285d94f4ea8d9836390a45360533',
-  'libunwind_revision': '43bb9f872232f531bac80093ceb4de61c64b9ab7',
+  'libcxx_revision': '78d6a7767ed57b50122a161b91f59f19c9bd0d19',
+  'libcxxabi_revision': '0d529660e32d77d9111912d73f2c74fc5fa2a858',
+  'libunwind_revision': '69d9b84cca8354117b9fe9705a4430d789ee599b',
 }
 
 # Only these hosts are allowed for dependencies in this DEPS file.
@@ -381,16 +381,13 @@ deps = {
     'condition': 'host_os == "mac"',
   },
   'src/buildtools/third_party/libc++/trunk':
-    Var('chromium_git') +
-    '/external/github.com/llvm/llvm-project/libcxx.git' + '@' +
+    Var('chromium_git') + '/chromium/llvm-project/libcxx.git' + '@' +
     Var('libcxx_revision'),
   'src/buildtools/third_party/libc++abi/trunk':
-    Var('chromium_git') +
-    '/external/github.com/llvm/llvm-project/libcxxabi.git' + '@' +
+    Var('chromium_git') + '/chromium/llvm-project/libcxxabi.git' + '@' +
     Var('libcxxabi_revision'),
   'src/buildtools/third_party/libunwind/trunk':
-    Var('chromium_git') +
-    '/external/github.com/llvm/llvm-project/libunwind.git' + '@' +
+    Var('chromium_git') + '/external/llvm.org/libunwind.git' + '@' +
     Var('libunwind_revision'),
   'src/buildtools/win': {
     'packages': [

buildtools/DEPS

@@ -18,9 +18,9 @@ vars = {
 
   # When changing these, also update the svn revisions in deps_revisions.gni
   'clang_format_revision': '96636aa0e9f047f17447f2d45a094d0b59ed7917',
-  'libcxx_revision':       'd9040c75cfea5928c804ab7c235fed06a63f743a',
-  'libcxxabi_revision':    '196ba1aaa8ac285d94f4ea8d9836390a45360533',
-  'libunwind_revision':    '43bb9f872232f531bac80093ceb4de61c64b9ab7',
+  'libcxx_revision':       '78d6a7767ed57b50122a161b91f59f19c9bd0d19',
+  'libcxxabi_revision':    '0d529660e32d77d9111912d73f2c74fc5fa2a858',
+  'libunwind_revision':    '69d9b84cca8354117b9fe9705a4430d789ee599b',
 }
 
 deps = {
@@ -48,16 +48,13 @@ deps = {
     'condition': 'host_os == "mac"',
   },
   'third_party/libc++/trunk':
-    Var('chromium_url') +
-    '/external/github.com/llvm/llvm-project/libcxx.git' + '@' +
+    Var('chromium_url') + '/chromium/llvm-project/libcxx.git' + '@' +
     Var('libcxx_revision'),
   'third_party/libc++abi/trunk':
-    Var('chromium_url') +
-    '/external/github.com/llvm/llvm-project/libcxxabi.git' + '@' +
+    Var('chromium_url') + '/chromium/llvm-project/libcxxabi.git' + '@' +
     Var('libcxxabi_revision'),
   'third_party/libunwind/trunk':
-    Var('chromium_url') +
-    '/external/github.com/llvm/llvm-project/libunwind.git' + '@' +
+    Var('chromium_url') + '/external/llvm.org/libunwind.git' + '@' +
     Var('libunwind_revision'),
   'win': {
     'packages': [