all: fix or silence various gcc warnings

As usual, gcc finds some real problems but also reports a ton
of noise. Fix the problems and quiet the noise.

src/cmd/paint/eenter.c

@@ -78,6 +78,7 @@ eenter(char *ask, char *buf, int len, Mouse *m)
 	b = screen;
 	sc = b->clipr;
 	replclipr(b, 0, b->r);
+	t = ZP;
 
 	while(!done){
 		p = stringsize(font, buf ? buf : "");