internal/rosa: flex artifact

Required by dtc, which is required by qemu.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/rosa/all.go

@@ -22,6 +22,7 @@ const (
 	Curl
 	Diffutils
 	Findutils
+	Flex
 	Fuse
 	GMP
 	GLib
@@ -129,6 +130,7 @@ func ResolveName(name string) (p PArtifact, ok bool) {
 		"curl":              Curl,
 		"diffutils":         Diffutils,
 		"findutils":         Findutils,
+		"flex":              Flex,
 		"fuse":              Fuse,
 		"gmp":               GMP,
 		"glib":              GLib,