target/109944 - avoid STLF fail for V16QImode CTOR expansion

target/109944 - avoid STLF fail for V16QImode CTOR expansion

The following dispatches to V2DImode CTOR expansion instead of
using sets of (subreg:DI (reg:V16QI 146) [08]) which causes
LRA to spill DImode and reload V16QImode.  The same applies for
V8QImode or V4HImode construction from SImode parts which happens
during 32bit libgcc build.

	PR target/109944
	* config/i386/i386-expand.cc (ix86_expand_vector_init_general):
	Perform final vector composition using
	ix86_expand_vector_init_general instead of setting
	the highpart and lowpart which causes spilling.

	* gcc.target/i386/pr109944-1.c: New testcase.
	* gcc.target/i386/pr109944-2.c: Likewise.