libgo: move golang.org/x/sync/semaphore to gotool packages

golang/x/sync/semaphore is required by gofmt.go.

Change-Id: Ib8512620cde5311b79d8cca405b723f77f685d3c
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/388634
Reviewed-by: Jeremy Faller <jeremy@golang.org>
Trust: Jeremy Faller <jeremy@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>
Trust: Than McIntosh <thanm@google.com>

libgo/gotool-packages.txt

@@ -63,6 +63,7 @@ golang.org/x/mod/sumdb/dirhash
 golang.org/x/mod/sumdb/note
 golang.org/x/mod/sumdb/tlog
 golang.org/x/mod/zip
+golang.org/x/sync/semaphore
 golang.org/x/tools/go/analysis
 golang.org/x/tools/go/analysis/internal/analysisflags
 golang.org/x/tools/go/analysis/internal/facts

libgo/libgo-packages.txt

@@ -95,7 +95,6 @@ golang.org/x/net/http/httpproxy
 golang.org/x/net/http2/hpack
 golang.org/x/net/idna
 golang.org/x/net/nettest
-golang.org/x/sync/semaphore
 golang.org/x/sys/cpu
 golang.org/x/text/secure/bidirule
 golang.org/x/text/transform