rs6000, fix vec_replace_unaligned built-in arguments

The first argument of the vec_replace_unaligned built-in should always be
of type vector unsigned char, as specified in gcc/doc/extend.texi.

This patch fixes the builtin definitions and updates the test cases to use
the correct arguments.  The original test file is renamed and a second test
file is added for a new test case.

gcc/ChangeLog:
	* config/rs6000/rs6000-builtins.def: Rename
	__builtin_altivec_vreplace_un_uv2di as __builtin_altivec_vreplace_un_udi
	__builtin_altivec_vreplace_un_uv4si as __builtin_altivec_vreplace_un_usi
	__builtin_altivec_vreplace_un_v2df as __builtin_altivec_vreplace_un_df
	__builtin_altivec_vreplace_un_v2di as __builtin_altivec_vreplace_un_di
	__builtin_altivec_vreplace_un_v4sf as __builtin_altivec_vreplace_un_sf
	__builtin_altivec_vreplace_un_v4si as __builtin_altivec_vreplace_un_si.
	Rename VREPLACE_UN_UV2DI as VREPLACE_UN_UDI, VREPLACE_UN_UV4SI as
	VREPLACE_UN_USI, VREPLACE_UN_V2DF as VREPLACE_UN_DF,
	VREPLACE_UN_V2DI as VREPLACE_UN_DI, VREPLACE_UN_V4SF as
	VREPLACE_UN_SF, VREPLACE_UN_V4SI as VREPLACE_UN_SI.
	Rename vreplace_un_v2di as vreplace_un_di, vreplace_un_v4si as
	vreplace_un_si, vreplace_un_v2df as vreplace_un_df,
	vreplace_un_v2di as vreplace_un_di, vreplace_un_v4sf as
	vreplace_un_sf, vreplace_un_v4si as vreplace_un_si.
	* config/rs6000/rs6000-c.cc (find_instance): Add case
	RS6000_OVLD_VEC_REPLACE_UN.
	* config/rs6000/rs6000-overload.def (__builtin_vec_replace_un):
	Fix first argument type.  Rename VREPLACE_UN_UV4SI as
	VREPLACE_UN_USI, VREPLACE_UN_V4SI as VREPLACE_UN_SI,
	VREPLACE_UN_UV2DI as VREPLACE_UN_UDI, VREPLACE_UN_V2DI as
	VREPLACE_UN_DI, VREPLACE_UN_V4SF as VREPLACE_UN_SF,
	VREPLACE_UN_V2DF as VREPLACE_UN_DF.
	* config/rs6000/vsx.md (REPLACE_ELT): Rename the mode_iterator
	REPLACE_ELT_V for vector modes.
	(REPLACE_ELT): New scalar mode iterator.
	(REPLACE_ELT_char): Add scalar attributes.
	(vreplace_un_<mode>): Change iterator and mode attribute.

gcc/testsuite/ChangeLog:
	* gcc.target/powerpc/vec-replace-word-runnable.c: Renam
	vec-replace-word-runnable_1.c.
	* gcc.target/powerpc/vec-replace-word-runnable_1.c
	(dg-options): add -flax-vector-conversions.
	(vec_replace_unaligned) Fix first argument type.
	(vresult_uchar): Fix expected results.
	(vec_replace_unaligned): Update for loop to check uchar results.
	Remove extra spaces in if statements. Insert missing spaces in
	for statements.
	* gcc.target/powerpc/vec-replace-word-runnable_2.c: New test file.