clang-tidy/misc-sizeof-container.cpp: Add explicit triple.

For targeting LLP64, like Windows x86, size_t is not unsigned long.

  tools/clang/tools/extra/test/clang-tidy/Output/misc-sizeof-container.cpp.tmp.cpp:33:12: error: target of using declaration conflicts with declaration already in scope [clang-diagnostic-error]
  using std::size_t;
             ^

llvm-svn: 247394