C++: Fix crash in warn_for_memset within templates (PR c++/83814)

C++: Fix crash in warn_for_memset within templates (PR c++/83814)

gcc/c-family/ChangeLog:
	PR c++/83814
	* c-common.c (fold_for_warn): Move to c/c-fold.c and cp/expr.c.

gcc/c/ChangeLog:
	PR c++/83814
	* c-fold.c (fold_for_warn): Move from c-common.c, reducing to just
	the C part.

gcc/cp/ChangeLog:
	PR c++/83814
	* expr.c (fold_for_warn): Move from c-common.c, reducing to just
	the C++ part.  If processing a template, call
	fold_non_dependent_expr rather than fully folding.

gcc/testsuite/ChangeLog:
	PR c++/83814
	PR c++/83902
	* g++.dg/wrappers/pr83814.C: New test case.
	* g++.dg/wrappers/pr83902.C: New test case.

From-SVN: r256804