cmd/compile: fix recursive inimport handling

expandDecl can be called recursively, so it's not an appropriate place
to clean inimport. Instead, move this up to resolve, along with an
appropriate recursion check.

Passes toolstash-check.

Change-Id: I138d37b057dcc6525c780b4b3fbaa5e97f99655b
Reviewed-on: https://go-review.googlesource.com/120455
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

src/cmd/compile/internal/gc/iimport.go

@@ -46,9 +46,7 @@ func expandDecl(n *Node) {
 		return
 	}
 
-	inimport = true
 	r.doDecl(n)
-	inimport = false
 }
 
 func expandInline(fn *Node) {

src/cmd/compile/internal/gc/typecheck.go

@@ -37,7 +37,12 @@ func resolve(n *Node) *Node {
 	}
 
 	if n.Sym.Pkg != localpkg {
+		if inimport {
+			Fatalf("recursive inimport")
+		}
+		inimport = true
 		expandDecl(n)
+		inimport = false
 		return n
 	}