c: Fix constructor bounds checking for VLA and construct VLA vector constants

c: Fix constructor bounds checking for VLA and construct VLA vector constants

This patch adds support for checking bounds of SVE ACLE vector initialization
constructors.  It also adds support to construct vector constant from init
constructors.

gcc/c/ChangeLog:

	* c-typeck.cc (process_init_element): Add check to restrict
	constructor length to the minimum vector length allowed.

gcc/ChangeLog:

	* tree.cc (build_vector_from_ctor): Add support to construct VLA vector
	constants from init constructors.

gcc/testsuite/ChangeLog:

	* gcc.target/aarch64/sve/acle/general-c/sizeless-1.c: Update test to
	test initialize error.
	* gcc.target/aarch64/sve/acle/general-c/sizeless-2.c: Likewise.