Enable 32/64-bit gyp switch on Linux

Linux defaults to 64, other platforms 32.  As of this change, only Mac and
Linux are affected by the skia_arch_width flag.  Next step is to make Win
work as well.
Review URL: https://codereview.appspot.com/6460066

git-svn-id: http://skia.googlecode.com/svn/trunk@5041 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/gyp/common_conditions.gypi b/gyp/common_conditions.gypi
index 143e854..2b9800f 100644
--- a/gyp/common_conditions.gypi
+++ b/gyp/common_conditions.gypi
@@ -111,6 +111,24 @@
           '-Wno-unused-parameter',
           '-Wno-c++11-extensions'
         ],
+        'conditions' : [
+          ['skia_arch_width == 64', {
+            'cflags': [
+              '-m64',
+            ],
+            'ldflags': [
+              '-m64',
+            ],
+          }],
+          ['skia_arch_width == 32', {
+            'cflags': [
+              '-m32',
+            ],
+            'ldflags': [
+              '-m32',
+            ],
+          }],
+        ],
         'include_dirs' : [
           '/usr/include/freetype2',
         ],