clang/test/SemaCXX/err_init_conversion_failed.cpp: Tweak for i686-msvc.

For targeting i686-msvc, declarations are seen as thiscall like;

  void (template_test::S::*)(const int &) __attribute__((thiscall))
  void (template_test::S::*)(int) __attribute__((thiscall))

It didn't affect x86_64-msvc.