Make gflags available to recovery

To enable recovery on cuttlefish, we need socket_forward_proxy, which
uses libgflags.

Bug: 122316490
Change-Id: I77798768c03282670bcaf5a0dd6ad8890468db6f
diff --git a/Android.bp b/Android.bp
index 690232e..7bf43dc 100644
--- a/Android.bp
+++ b/Android.bp
@@ -2,6 +2,7 @@
     name: "libgflags",
     host_supported: true,
     vendor_available: true,
+    recovery_available: true,
     srcs: [
         "src/gflags.cc",
         "src/gflags_completions.cc",