backport: re PR target/87496 (ICE in aggregate_value_p at gcc/function.c:2046)

backport: re PR target/87496 (ICE in aggregate_value_p at gcc/function.c:2046)

gcc/
	Backport from mainline
	2018-12-07  Peter Bergner  <bergner@linux.ibm.com>

	PR target/87496
	* config/rs6000/rs6000.c (rs6000_option_override_internal): Disallow
	-mabi=ieeelongdouble and -mabi=ibmlongdouble without -mlong-double-128.
	Do not error for -mabi=ibmlongdouble and no ISA 2.06 support.
	* doc/invoke.texi: Document -mabi=ibmlongdouble and -mabi=ieeelongdouble
	require -mlong-double-128.

gcc/testsuite/
	Backport from mainline
	2018-12-07  Peter Bergner  <bergner@linux.ibm.com>

	PR target/87496
	* gcc.target/powerpc/pr87496-1.c: New test.
	* gcc.target/powerpc/pr87496-2.c: New test.
	* gcc.target/powerpc/pr87496-3.c: New test.

From-SVN: r267062