gc: use octal escapes in mkopnames

Plan 9's tr(1) doesn't accept the C-style escapes
for tab and newline characters.  I was going to use
the \xFF hexadecimal escapes but GNU tr(1) doesn't
accept those.  It seems octal is the least common
denominator.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/5576079

src/cmd/gc/mkopnames

@@ -14,8 +14,8 @@ echo '{'
 sed -n '/OXXX/,/OEND/p' go.h |
 	cpp |
 	sed 's!//.*!!; /^#/d'  |
-	tr ' ' '\n' |
-	tr -d ' \t,' |
+	tr ' ' '\012' |
+	tr -d ' \011,' |
 	grep . |
 	sort |
 	grep -v '^OEND$' |