test: in asmcheck, regexp must match from beginning of line
test: in asmcheck, regexp must match from beginning of line

This avoid simple bugs like "ADD" matching "FADD". Obviously
"ADD" will still match "ADDQ" so some care is still required
in this regard, but at least a first class of possible errors
is taken care of.

Change-Id: I7deb04c31de30bedac9c026d9889ace4a1d2adcb
Reviewed-on: https://go-review.googlesource.com/97817
Reviewed-by: Giovanni Bajo <387225cd66f97dc812a00599dbc5b6544a73295c@develer.com>
Reviewed-by: Keith Randall <8c99c3a9284e493be632950b84cd789d08ed3e9d@golang.org>

nawawi/go,CAFxX/go,codestation/go,cloudflare/go,cloudflare/go,golang/go,CAFxX/go,josharian/go,akutz/go,josharian/go,CAFxX/go,josharian/go,nawawi/go,golang/go,CAFxX/go,CAFxX/go,akutz/go,golang/go,golang/go,codestation/go,codestation/go,akutz/go,Cofyc/go,josharian/go,Cofyc/go,josharian/go,CAFxX/go,golang/go,cloudflare/go,cloudflare/go,codestation/go,nawawi/go,akutz/go,codestation/go,codestation/go,codestation/go,akutz/go,nawawi/go,cloudflare/go,josharian/go,nawawi/go,Cofyc/go,golang/go,Cofyc/go,akutz/go,cloudflare/go,cloudflare/go,cloudflare/go,Cofyc/go,akutz/go,golang/go,CAFxX/go,josharian/go,nawawi/go,Cofyc/go,josharian/go,nawawi/go,golang/go,CAFxX/go,nawawi/go,akutz/go,codestation/go,Cofyc/go,Cofyc/go