middle-end/95690 - avoid MEM_EXPRs for constants

middle-end/95690 - avoid MEM_EXPRs for constants

The following avoids calling set_mem_attributes on the
DECL_INITIAL of a CONST_DECL which seems pointless since there
cannot be a sensible MEM_EXPR derived from that.  We're overwriting
both other possibly useful info, alias-set and alignment immediately
so the following patch simply removes the call instead of making
the function deal with even more (unexpected) trees that are not
memory accesses.

2020-06-16  Richard Biener  <rguenther@suse.de>

	PR middle-end/95690
	* varasm.c (build_constant_desc): Remove set_mem_attributes call.

	* gfortran.dg/pr95690.f90: New testcase.