Roll Clang r170392:r174491.

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index 63a569c7e2b28ac5873c8f276658b18b51ebfd28..2c433bceaa0db45345dec1c574e64b0f86c03613 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -2787,6 +2787,10 @@
               # Warns on switches on enums that cover all enum values but
               # also contain a default: branch. Chrome is full of that.
               '-Wno-covered-switch-default',
+
+              # TODO(thakis,hans): Remove once Clang doesn't warn about false
+              # positives in our code.
+              '-Wno-undefined-internal',
             ],
             'cflags!': [
               # Clang doesn't seem to know know this flag.
@@ -3371,6 +3375,10 @@
                 # Warns on switches on enums that cover all enum values but
                 # also contain a default: branch. Chrome is full of that.
                 '-Wno-covered-switch-default',
+
+                # TODO(thakis,hans): Remove once Clang doesn't warn about false
+                # positives in our code.
+                '-Wno-undefined-internal',
               ],
               'OTHER_CPLUSPLUSFLAGS': [
                 # gnu++11 instead of c++11 so that __ANSI_C__ doesn't get