make: Expose a 'linker_supports_icf' flag.

This will allow us to use the flag in some build configurations of Chrome.
Review URL: http://codereview.chromium.org/6883065

git-svn-id: http://gyp.googlecode.com/svn/trunk@914 78cadc50-ecff-11dd-a971-7dbc132099af

pylib/gyp/generator/make.py

@@ -1259,6 +1259,13 @@ def RunSystemTests():
            'LINK_flags': link_flags }
 
 
+def CalculateVariables(default_variables, params):
+  """Calculate additional variables for use in the build (called by gyp)."""
+  cc_target = os.environ.get('CC.target', os.environ.get('CC', 'cc'))
+  default_variables['LINKER_SUPPORTS_ICF'] = \
+      gyp.system_test.TestLinkerSupportsICF(cc_command=cc_target)
+
+
 def GenerateOutput(target_list, target_dicts, data, params):
   options = params['options']
   generator_flags = params.get('generator_flags', {})

pylib/gyp/system_test.py

@@ -57,6 +57,13 @@ def TestLinkerSupportsThreads(cc_command='cc'):
                       env={'cc': cc_command})
 
 
+def TestLinkerSupportsICF(cc_command='cc'):
+  """Test whether the linker supports identical code folding."""
+  return TestCommands(['%(cc)s -Wl,--icf=safe test.c'],
+                      files={'test.c': 'int main(){}'},
+                      env={'cc': cc_command})
+
+
 if __name__ == '__main__':
   # Run the various test functions and print the results.
   def RunTest(description, function, **kwargs):