[NaCl SDK] Fix location of gmock and gtest libraries

This fixes the SDK build which was broken when these
libraries were moved.

BUG=724707

Review-Url: https://codereview.chromium.org/2896703005
Cr-Commit-Position: refs/heads/master@{#473730}

native_client_sdk/src/libraries/gmock/library.dsc

 {
-      #   gmock-spec-builders.cc:248: error: enumeration value ‘FAIL’ not handled in switch
-      #'CXXFLAGS': ['-Wno-switch-enum'],
   'SEARCH': [
-    '../../../../testing/gmock',
+    '../../../../third_party/googletest/src/googlemock',
   ],
   'DATA': [
     'src/gmock.cc',

native_client_sdk/src/libraries/gtest/library.dsc

 {
   'SEARCH': [
-    '../../../../testing/gtest',
+    '../../../../third_party/googletest/src/googletest',
   ],
   'DATA': [
     'src/gtest.cc',