make: Expose a 'linker_supports_icf' flag.

pylib/gyp/system_test.py

Index: pylib/gyp/system_test.py
===================================================================
--- pylib/gyp/system_test.py	(revision 913)
+++ pylib/gyp/system_test.py	(working copy)
@@ -57,6 +57,13 @@
                       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):