[Support] Fix warnings

This patch fixes:

  third-party/unittest/googletest/include/gtest/gtest.h:1379:11:
  error: comparison of integers of different signs: 'const int' and
  'const unsigned int' [-Werror,-Wsign-compare]

  llvm/unittests/Support/CommandLineTest.cpp:2294:3: note: in
  instantiation of function template specialization
  'testing::internal::EqHelper::Compare<int, unsigned int, nullptr>'
  requested here