asmtest: avoid testing against complex nop alignment in gas

asmtest: avoid testing against complex nop alignment in gas

.align #,0x90 in gas ignores the 0x90 and outputs any kind
of nop it feels like.  the one avoided by this patch is a 7
byte nop, which gas has been doing since at least 1999:
http://sourceware.org/ml/binutils/1999-10/msg00083.html

In order to match what gas does, we would need to make
code alignment target-specific, import a lot of code, and
face the question: exactly which gas {version,target,tune}
combo are we trying to match?  see i386_align_code in:
http://sourceware.org/cgi-bin/cvsweb.cgi/src/gas/config/tc-i386.c?annotate=1.460&cvsroot=src

The smart noppery is turned on via the special casing of 0x90
at line 438 in md_do_align in:
http://sourceware.org/cgi-bin/cvsweb.cgi/src/gas/config/tc-i386.h?annotate=1.1&cvsroot=src