rs6000, remove __builtin_vsx_xvcmp* built-ins

rs6000, remove __builtin_vsx_xvcmp* built-ins

This patch removes the built-ins:
 __builtin_vsx_xvcmpeqsp, __builtin_vsx_xvcmpgesp,
 __builtin_vsx_xvcmpgtsp.

which are similar to the recommended PVIPR documented overloaded
vec_cmpeq, vec_cmpgt and vec_cmpge built-ins.

The difference is that the overloaded built-ins return a vector of
32-bit booleans.  The removed built-ins returned a vector of floats.

The __builtin_vsx_xvcmpeqdp, __builtin_vsx_xvcmpgedp and
__builtin_vsx_xvcmpgtdp are not removed as they are used by the
overloaded vec_cmpeq, vec_cmpgt and vec_cmpge built-ins.

The test cases for the __builtin_vsx_xvcmpeqsp, __builtin_vsx_xvcmpgesp,
__builtin_vsx_xvcmpgtsp, __builtin_vsx_xvcmpeqdp,
__builtin_vsx_xvcmpgedp and __builtin_vsx_xvcmpgtdp  are changed to use
the overloaded vec_cmpeq, vec_cmpgt, vec_cmpge built-ins.  Use of the
overloaded built-ins requires the result to be stored in a vector of
boolean of the appropriate size or the result must be cast to the return
type used by the original __builtin_vsx_xvcmp* built-ins.

gcc/ChangeLog:
	* config/rs6000/rs6000-builtins.def (__builtin_vsx_xvcmpeqsp,
	__builtin_vsx_xvcmpgesp, __builtin_vsx_xvcmpgtsp): Remove
	definitions.

gcc/testsuite/ChangeLog:
	* gcc.target/powerpc/vsx-builtin-3.c (do_cmp): Replace
	__builtin_vsx_xvcmp{eq,gt,ge}{sp,dp} by vec_cmp{eq,gt,ge}
	respectively and add explicit casts to vector {float,double}.
	Add more testing code assigning result to vector boolean types.