[NaCl SDK] Get nacl_mounts_tests building.

native_client_sdk/src/libraries/gtest/library.dsc

 {
   'TOOLS': ['newlib', 'glibc', 'pnacl', 'win'],
   'SEARCH': [
+    '.',
     '../../../../testing/gtest/include/gtest',
     '../../../../testing/gtest/include/gtest/internal',
     '../../../../testing/gtest/src',
   ],
   'TARGETS': [
     {
       'NAME' : 'gtest',
       'TYPE' : 'lib',
       'SOURCES' : [
         'gtest.cc',
         'gtest-death-test.cc',
         'gtest-filepath.cc',
         'gtest_main.cc',
         'gtest-port.cc',
         'gtest-printers.cc',
         'gtest-test-part.cc',
         'gtest-typed-test.cc',
+        'nacl_gtest_dummy_sys.cc',
       ],
       # Ignore warning:
       #   gtest.cc:2555: error: enumeration value ‘COLOR_DEFAULT’ not handled in switch
       'CXXFLAGS': ['-Wno-switch-enum'],
       'INCLUDES': [
         # See comment below about gtest-internal-inl.h
         '$(NACL_SDK_ROOT)/include/gtest/internal',
       ],
     }
   ],
@@ skipping 37 matching lines @@
       'FILES': [
         'gtest-internal-inl.h',
       ],
       'DEST': 'include/gtest/internal/src',
     },
   ],
   'DEST': 'testing',
   'NAME': 'gtest',
   'EXPERIMENTAL': True,
 }