[build, libgo, libstdc++] Build libgo with -Wa,-nH if possible (PR go/78978)

[Jonathan Wakely]

On 05/01/17 10:20 +0100, Rainer Orth wrote:
>As could have been expected, the static libgo.a causes the same problem
>with hardware capabilities on Solaris/x86 as was solved for libgo.so
>with
>
>	https://gcc.gnu.org/ml/gcc-patches/2016-12/msg00726.html
>
>Instead of trying to pass -mclear-hwcap with -static-libgo, it was
>deemed easier to solve both problems the same way and disable hwcaps
>support in the assembler in the first place.
>
>This has already been done in libstdc++, so I've moved the corresponding
>autoconf macro to config/hwcaps.m4 and adapted it to set HWCAP_CFLAGS
>instead of HWCAP_FLAGS to better differntiate from HWCAP_LDFLAGS.
>Everything else is straightforward, I believe.
>
>Bootstrapped without regressions on i386-pc-solaris2.1[02] with as/ld
>(where as supports -nH) and sparc-sun-solaris2.12 with as/ld (where as
>doesn't, or rather it's called -hwcap={1|0}), and the libgo
>runtime/pprof failure is gone.
>
>Ok for mainline?

I can't approve the whole thing, but moving the macro out of libstdc++
is OK.