libcpp: use better locations for _Pragma tokens (preprocessor/69126)

libcpp: use better locations for _Pragma tokens (preprocessor/69126)

gcc/testsuite/ChangeLog:
	PR preprocessor/69126
	* c-c++-common/pr69126.c: New test case.

libcpp/ChangeLog:
	PR preprocessor/69126
	* directives.c (destringize_and_run): Add expansion_loc param; use
	it when handling unexpanded pragmas to fixup the locations of the
	synthesized tokens.
	(_cpp_do__Pragma): Add expansion_loc param and use it when calling
	destringize_and_run.
	* internal.h (_cpp_do__Pragma): Add expansion_loc param.
	* macro.c (builtin_macro): Pass expansion location of _Pragma to
	_cpp_do__Pragma.

From-SVN: r232893