linux/clang: Disable the last two warnings, turn on -Werror

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index c85107eb74eb9913dbe8b131a10b327d155efc70..7fd9f21b3a6f2d9c06ebb52a66cdf6edb3a6db0b 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -1618,7 +1618,6 @@
             'cflags!': [
               '-Wall',
               '-Wextra',
-              '-Werror',
             ],
             'cflags_cc': [
               # Don't warn about hash_map in third-party code.
@@ -1635,6 +1634,12 @@
               '-Wsign-compare',
             ]
           }],
+          # TODO: Fix all warnings on chromeos too.
+          [ 'os_posix==1 and OS!="mac" and OS!="ios" and (clang!=1 or chromeos==1)', {
+            'cflags!': [
+              '-Werror',
+            ],
+          }],
           [ 'os_posix==1 and os_bsd!=1 and OS!="mac" and OS!="android"', {
             'cflags': [
               # Don't warn about ignoring the return value from e.g. close().