Use the experimental PBQP register allocator for UBSan builds.

This decreases compile time, so we don't need to build certain libraries with -O0 anymore (and we can't because PBQP doesn't support -O0)

BUG=426271
TBR=inferno@chromium.org

Review URL: https://codereview.chromium.org/715633004

Cr-Commit-Position: refs/heads/master@{#303657}

build/common.gypi

@@ -4214,6 +4214,13 @@
                   '-fsanitize=undefined',
                   # -fsanitize=vptr is incompatible with -fno-rtti.
                   '-fno-sanitize=vptr',
+                  # Employ the experimental PBQP register allocator to avoid
+                  # slow compilation on files with too many basic blocks.
+                  # See http://crbug.com/426271.
+                  '-mllvm -regalloc=pbqp',
+                  # Speculatively use coalescing to slightly improve the code
+                  # generated by PBQP regallocator. May increase compile time.
+                  '-mllvm -pbqp-coalescing',
                 ],
                 'ldflags': [
                   '-fsanitize=undefined',

third_party/mesa/mesa.gyp

@@ -657,14 +657,6 @@
             '_GLAPI_NO_EXPORTS',
           ],
         }],
-        ['ubsan==1', {
-          # Due to a bug in LLVM (http://llvm.org/bugs/show_bug.cgi?id=21349),
-          # compilation hangs for some Mesa source files. Disable -O2
-          # temporarily until http://crbug.com/426271 is fixed.
-          'cflags!': [
-            '-O2',
-          ],
-        }],
       ],
     },
     # Building this target will hide the native OpenGL shared library and

ui/gl/gl.gyp

@@ -312,14 +312,6 @@
             '../android/ui_android.gyp:ui_java',
           ],
         }],
-        ['ubsan==1', {
-          # Due to a bug in LLVM (http://llvm.org/bugs/show_bug.cgi?id=21349),
-          # compilation hangs for some GL source files. Disable -O2 temporarily
-          # until http://crbug.com/426271 is fixed.
-          'cflags!': [
-            '-O2',
-          ],
-        }],
       ],
     },
     {