Fix build warnings with gcc4.8

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index 0fe8b73a27892551156cd5ee253a5398b17a5165..de0c1a3387a135a831af56ed658607dbdcfab296 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -2558,6 +2558,16 @@
           '-fvisibility=hidden',
           '-pipe',
         ],
+        'conditions': [

[qiankun, 2013/04/13 01:21:30]

  Add a conditions section to check if gcc_version>=48. But it seems this
conditions section doesn't work. Because this flag doesn't appear in the
generated *.mk files. 
  If use 'target_conditions' instead of 'conditions', got the following error
"gyp: name 'gcc_version' is not defined while evaluating condition
'gcc_version>=48' in src/v8/tools/gyp/v8.gyp".
  If use the following code, it works.
        'target_conditions': [
          # Don't warn about the "typedef 'foo' locally defined but not used"
          # for gcc 4.8.
          # TODO: remove this flag once all builds work. See crbug.com/227506
          [ '1==1', {
            'cflags': [
              '-Wno-unused-local-typedefs',
            ],
          }],
        ],
   Could you give some comments on these problems? What's the correct method to
check gcc_version here?

[Raphael Kubo da Costa (rakuco), 2013/04/15 10:57:07]

Have you tried running `gyp_chromium' with the CHROMIUM_GYP_SYNTAX_CHECK
environment variable set? I think the problem with putting this section here is
that there's also a `conditions' section defined later (around line 2706). I
don't really know what's wrong with the `target_conditions' part.

In any case, it should all work if you just add this check to the existing
`conditions' section.

+          # Don't warn about the "typedef 'foo' locally defined but not used"
+          # for gcc 4.8.
+          # TODO: remove this flag once all builds work. See crbug.com/227506
+          [ 'gcc_version>=48', {
+            'cflags': [
+              '-Wno-unused-local-typedefs',
+            ],
+          }],
+        ],
         'cflags_cc': [
           '-fno-rtti',
           '-fno-threadsafe-statics',