cmd/link: avoid leaking file in ldshlibsyms

Change-Id: If27f7fbf94ede6f9a57f2520aaf75e6506e0b3f8
Reviewed-on: https://go-review.googlesource.com/59374
Run-TryBot: Dave Cheney <dave@cheney.net>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Dave Cheney <dave@cheney.net>

src/cmd/link/internal/ld/lib.go

@@ -1562,6 +1562,7 @@ func ldshlibsyms(ctxt *Link, shlib string) {
 		Errorf(nil, "cannot open shared library: %s", libpath)
 		return
 	}
+	defer f.Close()
 
 	hash, err := readnote(f, ELF_NOTE_GO_NAME, ELF_NOTE_GOABIHASH_TAG)
 	if err != nil {