Add libraries to fix Ubuntu13 Clang build

gyp/common_conditions.gypi

 # conditions used in both common.gypi and skia.gyp in chromium
 #
 {
   'defines': [
     'SK_ALLOW_STATIC_GLOBAL_INITIALIZERS=<(skia_static_initializers)',
   ],
   'conditions' : [
     [ 'skia_gpu == 1',
       {
         'defines': [
@@ skipping 229 matching lines @@
               'SK_BUILD_FOR_NACL',
             ],
             'link_settings': {
               'libraries': [
                 '-lppapi',
                 '-lppapi_cpp',
                 '-lnosys',
                 '-pthread',
               ],
             },
+          }, { # skia_os != "nacl"
+            'link_settings': {
+              'ldflags': [
+                '-lstdc++',
+                '-lm',
+              ],
+            },
           }],
-          [ 'skia_os == "chromeos"', {
-            'ldflags': [
-              '-lstdc++',
-              '-lm',
-            ],
-          }, {
+          [ 'skia_os != "chromeos"', {
             'conditions': [
               [ 'skia_arch_width == 64 and skia_arch_type == "x86"', {
                 'cflags': [
                   '-m64',
                 ],
                 'ldflags': [
                   '-m64',
                 ],
               }],
               [ 'skia_arch_width == 32 and skia_arch_type == "x86"', {
@@ skipping 212 matching lines @@
   'xcode_settings': {
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }
 
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