This fixes problems with tests that exceed a data type or the maximum stack frame...

This fixes problems with tests that exceed a data type or the maximum stack frame size on 16 bit targets.

Note: GCC has a limitation that a stack frame cannot exceed half the address space.

For two tests the decision to modify or skip them seems not so clear-cut;
I choose to modify gcc.dg/pr47893.c to use types that fit the numbers, as
that seemed to have little impact on the test, and skip gcc.dg/pr115646.c
for 16 bit, as layout of structs with bitfields members can have quite
subtle rules.

gcc/testsuite/
	* gcc.dg/pr107523.c: Make sure variables can fit numbers.
	* gcc.dg/pr47893.c: Add dg-require-effective-target size20plus clause.
	* c-c++-common/torture/builtin-clear-padding-2.c:
	dg-require-effective-target size20plus.
	* gcc.dg/pr115646.c: dg-require-effective-target int32plus.
	* c-c++-common/analyzer/coreutils-sum-pr108666.c:
	For c++, expect a warning about exceeding maximum object size
	if not size20plus.
	* gcc.dg/torture/inline-mem-cpy-1.c:
	Like the included file, dg-require-effective-target ptr32plus.
	* gcc.dg/torture/inline-mem-cmp-1.c: Likewise.