Fortran: Fix ICE with use of c_associated.

	PR fortran/120049

gcc/fortran/ChangeLog:

	* check.cc (gfc_check_c_associated): Modify checks to avoid
	ICE and allow use, intrinsic :: iso_c_binding from a separate
	module file.

gcc/testsuite/ChangeLog:

	* gfortran.dg/pr120049_a.f90: New test.
	* gfortran.dg/pr120049_b.f90: New test.

(cherry picked from commit d0571638a6bad932b226ada98b167fa47a47d838)