omp-offload.cc: Fix value-expr handling of 'declare target link' vars [PR115637]

omp-offload.cc: Fix value-expr handling of 'declare target link' vars [PR115637]

As the PR and included testcase shows, replacing 'arr2' by its value expression
'*arr2$13$linkptr' failed for
  MEM <uint128_t> [(c_char * {ref-all})&arr2]
which left 'arr2' in the code as unknown symbol. Now expand the value expression
already in pass_omp_target_link::execute's process_link_var_op walk_gimple_stmt
walk - and don't rely on gimple_regimplify_operands.

	PR middle-end/115637

gcc/ChangeLog:

	* gimplify.cc (gimplify_body): Fix macro name in the comment.
	* omp-offload.cc (find_link_var_op): Rename to ...
	(process_link_var_op): ... this. Replace value expr.
	(pass_omp_target_link::execute): Update walk_gimple_stmt call.

libgomp/ChangeLog:

	* testsuite/libgomp.fortran/declare-target-link.f90: Uncomment
	now working code.

Co-authored-by: Richard Biener <rguenther@suse.de