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

[Ian Lance Taylor]

On Thu, Jan 5, 2017 at 1:20 AM, Rainer Orth <ro@cebitec.uni-bielefeld.de> 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?
>
> Once approved, how should we proceed with checking?  Ian, will you take
> care of the libgo part once the rest is in?

This patch is OK.  Yes, please commit the config and libstdc++
portions.  Then I will commit the libgo portions to the external repo
and mirror them in.  Thanks.

Ian