rs6000, extend the current vec_{un,}signed{e,o} built-ins

rs6000, extend the current vec_{un,}signed{e,o} built-ins

The built-ins __builtin_vsx_xvcvspsxds and __builtin_vsx_xvcvspuxds
convert a vector of floats to a vector of signed/unsigned long long ints.
Extend the existing vec_{un,}signed{e,o} built-ins to handle the argument
vector of floats to return a vector of even/odd signed/unsigned integers.

The define expands vsignede_v4sf, vsignedo_v4sf, vunsignede_v4sf,
vunsignedo_v4sf are added to support the new vec_{un,}signed{e,o}
built-ins.

The built-ins __builtin_vsx_xvcvspsxds and __builtin_vsx_xvcvspuxds are
now for internal use only. They are not documented and they do not
have test cases.

Add testcases and update documentation.

gcc/ChangeLog:
	* config/rs6000/rs6000-builtins.def (__builtin_vsx_xvcvspsxds,
	__builtin_vsx_xvcvspuxds): Rename to __builtin_vsignede_v4sf,
	__builtin_vunsignede_v4sf respectively.
	(XVCVSPSXDS, XVCVSPUXDS): Rename to VEC_VSIGNEDE_V4SF,
	VEC_VUNSIGNEDE_V4SF respectively.
	(__builtin_vsignedo_v4sf, __builtin_vunsignedo_v4sf): New
	built-in definitions.
	* config/rs6000/rs6000-overload.def (vec_signede, vec_signedo,
	vec_unsignede, vec_unsignedo): Add new overloaded specifications.
	* config/rs6000/vsx.md (vsignede_v4sf, vsignedo_v4sf,
	vunsignede_v4sf, vunsignedo_v4sf): New define_expands.
	* doc/extend.texi (vec_signedo, vec_signede, vec_unsignedo,
	vec_unsignede): Add documentation for new overloaded built-ins to
	convert vector float to vector {un,}signed long long.

gcc/testsuite/ChangeLog:
	* gcc.target/powerpc/builtins-3-runnable.c
	(test_unsigned_int_result, test_ll_unsigned_int_result): Add
	new argument.
	(vec_signede, vec_signedo, vec_unsignede, vec_unsignedo): New
	tests for the overloaded built-ins.