i386: Make -march=x86-64-v[234] behave more like other -march= options

i386: Make -march=x86-64-v[234] behave more like other -march= options

If somebody has -march=x86-64-v2 (or -v3 or -v4) in $CFLAGS, $CXXFLAGS etc.,
then -m32 or -mabi=ms stops working.
What is worse, if one configures gcc --with-arch-64=x86-64-v2 (or -v3 or -v4),
then -mabi=ms stops working.

I think that is a nightmare user experience.  It is ok that x86-64-v[234]
behave slightly different from other -march= options (in that they imply
unless overridden -mtune=generic rather then -mtune= equal to the -march
argument), but the error when one mixes it with -mabi=ms, or -m32 doesn't
improve anything.
It is true that the exact option set is only defined in the x86-64 psABI
(IMHO that is a mistake too, we should copy that into the GCC documentation
like we document it for any other -march= option), but there is no reason
why that exact set of CPU features can't be used for other ABIs, it is just
a set of CPU features.  If we add micro-architecture levels to the 32-bit
ABI (I doubt anyone wants to do that, but just hypothetically), then those
micro-architecture levels wouldn't certainly be called x86-64-v* but perhaps
i386-v*.
In the tests, __GCC_HAVE_SYNC_COMPARE_AND_SWAP_16 can't be expected on -m32
not because the CPU feature wouldn't be set, but because the instruction
is 64-bit only and 32-bit code doesn't have __int128 etc. support.

2020-12-15  Jakub Jelinek  <jakub@redhat.com>

	* config/i386/i386-options.c (ix86_option_override_internal): Don't
	error on -march=x86-64-v[234] with -m32 or -mabi=ms.
	* config.gcc: Don't reject --with-arch=x86-64-v[234] or
	--with-arch_32=x86-64-v[234].
	* doc/invoke.texi (-march=x86-64-v[234]): Document what the option
	does for other ABIs.

	* gcc.target/i386/x86-64-v2.c: Don't expect
	__GCC_HAVE_SYNC_COMPARE_AND_SWAP_16 to be defined with -m32.
	* gcc.target/i386/x86-64-v2-other.c: New test.
	* gcc.target/i386/x86-64-v2-msabi.c: New test.
	* gcc.target/i386/x86-64-v3.c: Fix a comment pasto.  Don't expect
	__GCC_HAVE_SYNC_COMPARE_AND_SWAP_16 to be defined with -m32.
	* gcc.target/i386/x86-64-v3-other.c: New test.
	* gcc.target/i386/x86-64-v3-msabi.c: New test.
	* gcc.target/i386/x86-64-v4.c:Don't expect
	__GCC_HAVE_SYNC_COMPARE_AND_SWAP_16 to be defined with -m32.
	* gcc.target/i386/x86-64-v4-other.c: New test.
	* gcc.target/i386/x86-64-v4-msabi.c: New test.