gdb/testsuite: make gdb.reverse/i386-avx-reverse.exp require avx

The test gdb.reverse/i386-avx-reverse.exp was assuming that if the CPU
was like x86, it would have AVX instructions because I didn't know how
to check for AVX instruction support explicitly.  This commit updates
that to use the pre-existing TCL proc have_avx.

Also update the comment at the top of the test, since it was a copy of a
different test.

Approved-By: Andrew Burgess <aburgess@redhat.com>
1 file changed