tree-optimization/109334: Improve computation for access attribute

tree-optimization/109334: Improve computation for access attribute

The fix for PR104970 restricted size computations to the case
where the access attribute was specified explicitly (no VLA).
It also restricted it to void pointers or elements with constant
sizes.  The second restriction is enough to fix the original bug.
Revert the first change to again allow size computations for VLA
parameters and for VLA parameters together with an explicit access
attribute.

gcc/ChangeLog:

	PR tree-optimization/109334
	* tree-object-size.cc (parm_object_size): Allow size
	computation for implicit access attributes.

gcc/testsuite/ChangeLog:

	PR tree-optimization/109334
	* gcc.dg/builtin-dynamic-object-size-0.c
	(test_parmsz_simple3): Supported again.
	(test_parmsz_external4): New test.
	* gcc.dg/builtin-dynamic-object-size-20.c: New test.
	* gcc.dg/pr104970.c: New test.