Pass pure constants verbatim in perlasm/x86_64-xlate.pl

(Imported from upstream's 10c639a8a56c90bec9e332c7ca76ef552b3952ac)

Change-Id: Ia8203eeae9d274249595a6e352ec2f77a97ca5d5
Reviewed-on: https://boringssl-review.googlesource.com/7227
Reviewed-by: David Benjamin <davidben@google.com>
diff --git a/crypto/perlasm/x86_64-xlate.pl b/crypto/perlasm/x86_64-xlate.pl
index 3ebb018..79c3c03 100755
--- a/crypto/perlasm/x86_64-xlate.pl
+++ b/crypto/perlasm/x86_64-xlate.pl
@@ -193,8 +193,11 @@
 	if ($gas) {
 	    # Solaris /usr/ccs/bin/as can't handle multiplications
 	    # in $self->{value}
-	    $self->{value} =~ s/(?<![\w\$\.])(0x?[0-9a-f]+)/oct($1)/egi;
-	    $self->{value} =~ s/([0-9]+\s*[\*\/\%]\s*[0-9]+)/eval($1)/eg;
+	    my $value = $self->{value};
+	    $value =~ s/(?<![\w\$\.])(0x?[0-9a-f]+)/oct($1)/egi;
+	    if ($value =~ s/([0-9]+\s*[\*\/\%]\s*[0-9]+)/eval($1)/eg) {
+	        $self->{value} = $value;
+	    }
 	    sprintf "\$%s",$self->{value};
 	} else {
 	    $self->{value} =~ s/(0b[0-1]+)/oct($1)/eig;