cc, ld: fix more gcc 4.3 -O2 compile bugs

same as https://golang.org/cl/152088
in more files.

Fixes #83.

R=r, r1
https://golang.org/cl/152091

src/cmd/cc/lex.c

@@ -411,8 +411,7 @@ lookup(void)
 		h += *p++;
 	}
 	n = (p - symb) + 1;
-	if((int32)h < 0)
-		h = ~h;
+	h &= 0xffffff;
 	h %= NHASH;
 	c = symb[0];
 	for(s = hash[h]; s != S; s = s->link) {

src/cmd/ld/go.c

@@ -42,8 +42,8 @@ hashstr(char *name)
 	h = 0;
 	for(cp = name; *cp; h += *cp++)
 		h *= 1119;
-	if(h < 0)
-		h = ~h;
+	// not if(h < 0) h = ~h, because gcc 4.3 -O2 miscompiles it.
+	h &= 0xffffff;
 	return h;
 }
 

src/cmd/ld/lib.c

@@ -384,8 +384,8 @@ lookup(char *symb, int v)
 	for(p=symb; c = *p; p++)
 		h = h+h+h + c;
 	l = (p - symb) + 1;
-	if(h < 0)
-		h = ~h;
+	// not if(h < 0) h = ~h, because gcc 4.3 -O2 miscompiles it.
+	h &= 0xffffff;
 	h %= NHASH;
 	for(s = hash[h]; s != S; s = s->link)
 		if(s->version == v)