[Bug libitm/53113] Build fails in x86_avx.cc if AVX disabled but supported by as (Solaris & Linux)

["nheghathivhistha at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53113

--- Comment #17 from David Kredba <nheghathivhistha at gmail dot com> ---
I can't bootstrap 4.9.0 snapshots without patch attached. My machine is Core2
Quad where are not any avx instructions available. All is compiled from sources
(Gentoo) but libitm x86_avx.lo crashes bootstrap. -march=native is by gcc
translated to core2 what is correct. 

I saw qt 4.8.5 qmake reporting AVX available too, which is wrong. After I used
-mno-avx it stopped doing it.

Gcc knows there is no avx. Binutils reports AVX instruction set support anyway
as supported - it can work with it in code. The fact that code produced will
not run on host system is not burning them looks like. I recompiled them with
-mno-avx to be sure that tests for AVX will fail but GNU as reports them an
thus libitm still crashes bootstrap.

In my opinion if gcc cannot trust GNU AS it should tell itsef to libitm
configure what instructions sets are really available.

I think that reproducing needs machine where CPU does not know what AVX is.

Thank you.