Revert local change to x86masm.pl.

We're not using the masm output (and upstream does not even support it).
Reduce unnecessary diff from upstream.

Change-Id: Ic0b0f804bd7ec1429b3b1f40746297b57dcfcef6
Reviewed-on: https://boringssl-review.googlesource.com/8517
Reviewed-by: Adam Langley <agl@google.com>

crypto/perlasm/x86masm.pl

@@ -82,7 +82,7 @@ TITLE	$_[0].asm
 IF \@Version LT 800
 ECHO MASM version 8.00 or later is strongly recommended.
 ENDIF
-.686
+.486
 .MODEL	FLAT
 OPTION	DOTNAME
 IF \@Version LT 800