fortran: Support clobbering of reference variables [PR41453]

fortran: Support clobbering of reference variables [PR41453]

This adds support for clobbering of variables passed by reference,
when the reference is forwarded to a subroutine as actual argument
whose associated dummy has the INTENT(OUT) attribute.
This was explicitly disabled by a condition added with
r9-3032-gee7fb0588c6361b4d77337ab0f7527be64fcdde2 and removing that
condition seems to work, as demonstrated by the new testcase.

	PR fortran/41453
	PR fortran/87395

gcc/fortran/ChangeLog:

	* trans-expr.cc (gfc_conv_procedure_call): Remove condition
	disabling clobber generation for dummy variables.  Remove
	obsolete comment.

gcc/testsuite/ChangeLog:

	* gfortran.dg/intent_optimize_6.f90: New test.