mac: Switch the default compiler to clang for everyone.

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index d5bd6d242afd957acd852c7a0342d5ecfe099e7d..242fb17033d980def68e8debf740bb46adb3e06d 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -561,6 +561,8 @@
       }],  # os_posix==1 and OS!="mac"
 
       ['OS=="mac"', {
+        # Enable clang on mac by default!

[Mark Mentovai, 2011/09/15 02:54:59]

LGTM!

+        'clang%': 1,
         'conditions': [
           # mac_product_name is set to the name of the .app bundle as it should
           # appear on disk.  This duplicates data from
@@ -579,14 +581,6 @@
           ['branding=="Chrome" and buildtype=="Official"', {
             'mac_breakpad%': 1,
             'mac_keystone%': 1,
-
-            # Official builds use clang, but only on m15+. Since there's just
-            # one buildbot config for the builder for m13, m14, and m15, this
-            # can't be defined in the buildbot config but is instead defined
-            # here (it was added after the m14 branch was cut). This is in the
-            # buildtype=="Official" section so that developers don't see it
-            # for their local builds.
-            'clang%': 1,
           }, { # else: branding!="Chrome" or buildtype!="Official"
             'mac_breakpad%': 0,
             'mac_keystone%': 0,
@@ -1660,6 +1654,8 @@
           # MACOSX_DEPLOYMENT_TARGET maps to -mmacosx-version-min
           'MACOSX_DEPLOYMENT_TARGET': '<(mac_deployment_target)',
           'PREBINDING': 'NO',                       # No -Wl,-prebind
+          # Keep pch files below xcodebuild/.
+          'SHARED_PRECOMPS_DIR': '$(CONFIGURATION_BUILD_DIR)/SharedPrecompiledHeaders',
           'USE_HEADERMAP': 'NO',
           'OTHER_CFLAGS': [
             '-fno-strict-aliasing',  # See http://crbug.com/32204