Fortran: Fix function decl's location [PR95847]

gcc/fortran/ChangeLog:

	PR fortran/95847
	* trans-decl.c (gfc_get_symbol_decl): Do not (re)set the location
	of an external procedure.
	(build_entry_thunks, generate_coarray_init, create_main_function,
	gfc_generate_function_code): Use fndecl's location in BIND_EXPR.

gcc/testsuite/ChangeLog:

	PR fortran/95847
	* gfortran.dg/coverage.f90: New test.