go/packages: ask for EmbedPatterns and EmbedFiles if needed

If the NeedEmbedPatterns or NeedEmbedFiles bits are set, then ask the go
command for the respective field in the JSON output. This fixes the
builder failure caused by golang.org/cl/393017

Change-Id: Ic659e59e7576141024c330f64201fe6c04edc032
Reviewed-on: https://go-review.googlesource.com/c/tools/+/401095
Run-TryBot: Michael Matloob <matloob@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Michael Matloob <matloob@golang.org>
diff --git a/go/packages/golist.go b/go/packages/golist.go
index fce4e5e..88f6915 100644
--- a/go/packages/golist.go
+++ b/go/packages/golist.go
@@ -870,6 +870,12 @@
 	if cfg.Mode&NeedModule != 0 {
 		addFields("Module")
 	}
+	if cfg.Mode&NeedEmbedFiles != 0 {
+		addFields("EmbedFiles")
+	}
+	if cfg.Mode&NeedEmbedPatterns != 0 {
+		addFields("EmbedPatterns")
+	}
 	return "-json=" + strings.Join(fields, ",")
 }