rs6000: Add scalar cfuged instruction

rs6000: Add scalar cfuged instruction

Add the centifuge-doubleword instruction and built-in access.

[gcc]

2020-05-11  Kelvin Nilsen  <kelvin@gcc.gnu.org>

	* config/rs6000/rs6000-builtin.def (BU_FUTURE_MISC_0): New
	#define.
	(BU_FUTURE_MISC_1): Likewise.
	(BU_FUTURE_MISC_2): Likewise.
	(BU_FUTURE_MISC_3): Likewise.
	(__builtin_cfuged): New built-in function definition.
	* config/rs6000/rs6000.md (UNSPEC_CFUGED): New constant.
	(cfuged): New insn.
	* doc/extend.texi (Basic PowerPC Built-in Functions Available for
	a Future Architecture): New subsubsection.

[gcc/testsuite]

2020-05-11  Kelvin Nilsen  <kelvin@gcc.gnu.org>

	* gcc.target.powerpc/cfuged-0.c: New test.
	* gcc.target.powerpc/cfuged-1.c: New test.