rs6000: Fix arguments for __builtin_altivec_tr_stxvrwx, __builtin_altivec_tr_stxvrhx

rs6000: Fix arguments for __builtin_altivec_tr_stxvrwx, __builtin_altivec_tr_stxvrhx

The third argument for __builtin_altivec_tr_stxvrhx should be short *
not int *.  Similarly, the third argument for __builtin_altivec_tr_stxvrwx
should be int * not short *.  This patch fixes the arguments in the two
builtins.

A runnable test case is added to test the __builtin_altivec_tr_stxvrbx,
__builtin_altivec_tr_stxvrhx, __builtin_altivec_tr_stxvrwx and
__builtin_altivec_tr_stxvrdx builtins.

gcc/
	* config/rs6000/rs6000-builtins.def (__builtin_altivec_tr_stxvrhx,
	__builtin_altivec_tr_stxvrwx): Fix type of third argument.

gcc/testsuite/
	* gcc.target/powerpc/builtin_altivec_tr_stxvr_runnable.c: New test
	for __builtin_altivec_tr_stxvrbx, __builtin_altivec_tr_stxvrhx,
	__builtin_altivec_tr_stxvrwx, __builtin_altivec_tr_stxvrdx.