rs6000, remove built-ins __builtin_vsx_set_1ti, __builtin_vsx_set_2df, __builtin_vsx_...

rs6000, remove built-ins __builtin_vsx_set_1ti, __builtin_vsx_set_2df, __builtin_vsx_set_2di

The built-ins set a value in a vector.  The same operation can be done
in C-code.  The assembly code generated from the C-code is as good or
better than the code generated by the built-ins.  With default
optimization the number of assembly generated for the two methods are
similar.  With -O3 optimization, the assembly generated for the two
approaches is identical for the 2DF and 2DI types.  The assembly for
the C-code version of the 1Ti requires one less assembly instruction.
It also only uses one load versus two loads for the built-in.

With the removal of the built-ins, there are no other uses of the
set built-in attribute.  The code associated with the set built-in
attribute is removed.

Finally, the testcase for the __builtin_vsx_set_2df is removed.  The
other built-ins do not have testcases.

gcc/ChangeLog:
	* config/rs6000/rs6000-builtin.cc (get_element_number,
	altivec_expand_vec_set_builtin): Remove functions.
	(rs6000_expand_builtin): Remove the if statement to call
	altivec_expand_vec_set_builtin.
	* config/rs6000/rs6000-builtins.def (__builtin_vsx_set_1ti,
	__builtin_vsx_set_2df, __builtin_vsx_set_2di): Remove the
	built-in definitions.
	* config/rs6000/rs6000-gen-builtins.cc (struct attrinfo):
	Remove the isset variable from the structure.
	(parse_bif_attrs): Remove the uses of the isset variable.

gcc/testsuite/ChangeLog:
	* gcc.target/powerpc/vsx-builtin-3.c: Remove test cases for the
	__builtin_vsx_set_2df built-in.