clang/test/Frontend/Weverything-and-remarks.cpp: Add explicit -target.

You could see unexpected result (*.tmp.err) with "-target x86_64-win32".

  Weverything-and-remarks.cpp:11:9: warning: 'char32_t' type specifier is incompatible with C++98 [-Wc++98-compat]
  typedef __char32_t char32_t;
          ^
  Weverything-and-remarks.cpp:12:27: error: typedef redefinition with different types ('unsigned long' vs 'unsigned long long')
  typedef long unsigned int size_t;
                            ^
  Weverything-and-remarks.cpp:19:62: warning: dynamic exception specifications are deprecated [-Wdeprecated]
    static void assign(char_type& __c1, const char_type& __c2) throw() {
                                                               ^~~~~~~
  Weverything-and-remarks.cpp:19:62: note: use 'noexcept' instead
    static void assign(char_type& __c1, const char_type& __c2) throw() {
                                                               ^~~~~~~
                                                               noexcept
  Weverything-and-remarks.cpp:25:46: warning: unused parameter '__n' [-Wunused-parameter]
                                        size_t __n) {
                                               ^
  3 warnings and 1 error generated.