I'd like to remove -many from the options passed by default to the
assembler, on the grounds that a gcc bug in instruction selection (eg.
emitting a power9 insn for -mcpu=power8) is better found at assembly
time than run time.

For now, just do this when --enable-checking or gcc is not a release.

This patch also emits .machine assembler directives for ELF targets
when functions are compiled for different cpus via attributes or
pragmas.  That's necessary when the initial -m<cpu> option passed to
the assembler doesn't enable the superset of all opcodes emitted, as
seen by a failure of gcc.target/powerpc/clone2.c without .machine
when building gcc for power8.

rs6000_machine_from_flags deliberately uses ISA_2_4_MASKS rather than
ISA_2_2_MASKS for power5 because "friz" and other similar instructions
enabled by gcc with TARGET_FPRND are enabled in gas by "-mpower5".
(gas -mpower5 supports power5+ too.)  rs6000-cpus.def puts
OPTION_MASK_FPRND in ISA_2_4_MASKS, so ISA_2_4_MASKS is the one to use
in deciding to pass "-mpower5" to gas.

O3-pr70130.c also failed on an earlier version of this patch (when
only testing one ISA bit to determine .machine).  This is a test for a
power7 vector bug, but on power8 hw check_vect_support_and_set_flags
passes -mpower8-vector which means the test isn't exercising the
original bug exactly.  I reckon that is wrong, and similary for other
vector testcases that ask for a specific cpu.  I've fixed it here by
explicitly passing -mno-power8-vector and similar vector options.

	* config/rs6000/rs6000.h (ASM_OPT_ANY): Define.
	(ASM_CPU_SPEC): Conditionally add -many.
	* config/rs6000/rs6000.c (rs6000_machine): New static var.
	(rs6000_machine_from_flags, emit_asm_machine): New functions..
	(rs6000_file_start): ..extracted from here, and modified to
	test all ISA bits.
	(rs6000_output_function_prologue): Emit .machine as necessary.
	* testsuite/gcc.target/powerpc/ppc32-abi-dfp-1.c: Don't use
	power mnemonics.
	* testsuite/gcc.dg/vect/O3-pr70130.c: Disable default options
	added by check_vect_support_and_set_flags.
	* testsuite/gcc.dg/vect/pr48765.c: Likewise.
	* testsuite/gfortran.dg/vect/pr45714-b.f: Likewise.

From-SVN: r271500