gc: inlining, allow empty bodies, fix _ arguments.

R=rsc
CC=golang-dev
https://golang.org/cl/5487077
diff --git a/test/cmp.go b/test/cmp.go
index f079c5d..d51a11a 100644
--- a/test/cmp.go
+++ b/test/cmp.go
@@ -8,7 +8,8 @@
 
 import "unsafe"
 
-func use(bool) {}
+var global bool
+func use(b bool) { global = b }
 
 func stringptr(s string) uintptr { return *(*uintptr)(unsafe.Pointer(&s)) }