rs6000: Enable vec_insert for P8 with rs6000_expand_vector_set_var_p8 [PR98093]

rs6000: Enable vec_insert for P8 with rs6000_expand_vector_set_var_p8 [PR98093]

Support P8 variable vec_insert and Update testcases' instruction count.

gcc/ChangeLog:

2021-01-22  Xionghu Luo  <luoxhu@linux.ibm.com>

	PR target/98093

	* config/rs6000/rs6000-c.c (altivec_resolve_overloaded_builtin):
	Generate ARRAY_REF(VIEW_CONVERT_EXPR) for P8 and later
	platforms.
	* config/rs6000/rs6000.c (rs6000_expand_vector_set_var): Update
	to call different path for P8 and P9.
	(rs6000_expand_vector_set_var_p9): New function.
	(rs6000_expand_vector_set_var_p8): New function.

gcc/testsuite/ChangeLog:

2021-01-22  Xionghu Luo  <luoxhu@linux.ibm.com>

	* gcc.target/powerpc/pr79251.p8.c: New test.
	* gcc.target/powerpc/fold-vec-insert-char-p8.c: Adjust
	instruction counts.
	* gcc.target/powerpc/fold-vec-insert-char-p9.c: Likewise.
	* gcc.target/powerpc/fold-vec-insert-double.c: Likewise.
	* gcc.target/powerpc/fold-vec-insert-float-p8.c: Likewise.
	* gcc.target/powerpc/fold-vec-insert-float-p9.c: Likewise.
	* gcc.target/powerpc/fold-vec-insert-int-p8.c: Likewise.
	* gcc.target/powerpc/fold-vec-insert-int-p9.c: Likewise.
	* gcc.target/powerpc/fold-vec-insert-longlong.c: Likewise.
	* gcc.target/powerpc/fold-vec-insert-short-p8.c: Likewise.
	* gcc.target/powerpc/fold-vec-insert-short-p9.c: Likewise.
	* gcc.target/powerpc/vsx-builtin-7.c: Likewise.