build: use gcc -Werror

Better to fix the warnings that we find.

R=iant
CC=golang-dev
https://golang.org/cl/4406042

src/cmd/5c/peep.c

@@ -1100,7 +1100,7 @@ copyu(Prog *p, Adr *v, Adr *s)
 		if(v->type == D_REG) {
 			if(v->reg <= REGEXT && v->reg > exregoffset)
 				return 2;
-			if(v->reg == REGARG)
+			if(v->reg == (uchar)REGARG)
 				return 2;
 		}
 		if(v->type == D_FREG)
@@ -1118,7 +1118,7 @@ copyu(Prog *p, Adr *v, Adr *s)
 
 	case ATEXT:	/* funny */
 		if(v->type == D_REG)
-			if(v->reg == REGARG)
+			if(v->reg == (uchar)REGARG)
 				return 3;
 		return 0;
 	}

src/cmd/5c/txt.c

@@ -400,6 +400,10 @@ regsalloc(Node *n, Node *nn)
 void
 regaalloc1(Node *n, Node *nn)
 {
+	if(REGARG < 0) {
+		fatal(n, "regaalloc1 and REGARG<0");
+		return;
+	}
 	nodreg(n, nn, REGARG);
 	reg[REGARG]++;
 	curarg = align(curarg, nn->type, Aarg1, nil);

src/cmd/6c/peep.c

@@ -797,7 +797,7 @@ copyu(Prog *p, Adr *v, Adr *s)
 		return 3;
 
 	case ACALL:	/* funny */
-		if(REGARG >= 0 && v->type == REGARG)
+		if(REGARG >= 0 && v->type == (uchar)REGARG)
 			return 2;
 
 		if(s != A) {
@@ -810,7 +810,7 @@ copyu(Prog *p, Adr *v, Adr *s)
 		return 3;
 
 	case ATEXT:	/* funny */
-		if(REGARG >= 0 && v->type == REGARG)
+		if(REGARG >= 0 && v->type == (uchar)REGARG)
 			return 3;
 		return 0;
 	}

src/cmd/6c/txt.c

@@ -436,8 +436,10 @@ regsalloc(Node *n, Node *nn)
 void
 regaalloc1(Node *n, Node *nn)
 {
-	if(REGARG < 0)
-		diag(n, "regaalloc1 and REGARG<0");
+	if(REGARG < 0) {
+		fatal(n, "regaalloc1 and REGARG<0");
+		return;
+	}
 	nodreg(n, nn, REGARG);
 	reg[REGARG]++;
 	curarg = align(curarg, nn->type, Aarg1, nil);

src/cmd/8c/peep.c

@@ -713,7 +713,7 @@ copyu(Prog *p, Adr *v, Adr *s)
 		return 3;
 
 	case ACALL:	/* funny */
-		if(REGARG >= 0 && v->type == REGARG)
+		if(REGARG >= 0 && v->type == (uchar)REGARG)
 			return 2;
 
 		if(s != A) {

src/cmd/8c/txt.c

@@ -397,6 +397,10 @@ regsalloc(Node *n, Node *nn)
 void
 regaalloc1(Node *n, Node *nn)
 {
+	if(REGARG < 0) {
+		fatal(n, "regaalloc1 and REGARG<0");
+		return;
+	}
 	nodreg(n, nn, REGARG);
 	reg[REGARG]++;
 	curarg = align(curarg, nn->type, Aarg1, nil);

src/quietgcc.bash

@@ -35,15 +35,10 @@ esac
 tmp=/tmp/qcc.$$.$USER.out
 $gcc -Wall -Wno-sign-compare -Wno-missing-braces \
 	-Wno-parentheses -Wno-unknown-pragmas -Wno-switch -Wno-comment \
+	-Werror \
 	"$@" >$tmp 2>&1
 status=$?
 egrep -v "$ignore" $tmp | uniq | tee $tmp.1
 
-# Make incompatible pointer type "warnings" stop the build.
-# Not quite perfect--we should remove the object file--but
-# a step in the right direction.
-if egrep 'incompatible pointer type' $tmp.1 >/dev/null; then
-	status=1
-fi
 rm -f $tmp $tmp.1
 exit $status