Allowlist external/gflags in bp2build

This is a transitive dep of some tests in internal

Change-Id: Ie716309ee8430b84600876e18b7bed02736672bb
Test: TH
diff --git a/android/allowlists/allowlists.go b/android/allowlists/allowlists.go
index 71c8d0e..056c1a8 100644
--- a/android/allowlists/allowlists.go
+++ b/android/allowlists/allowlists.go
@@ -145,6 +145,7 @@
 		"external/flatbuffers":                   Bp2BuildDefaultTrueRecursively,
 		"external/fmtlib":                        Bp2BuildDefaultTrueRecursively,
 		"external/fsverity-utils":                Bp2BuildDefaultTrueRecursively,
+		"external/gflags":                        Bp2BuildDefaultTrueRecursively,
 		"external/google-benchmark":              Bp2BuildDefaultTrueRecursively,
 		"external/googletest":                    Bp2BuildDefaultTrueRecursively,
 		"external/guava":                         Bp2BuildDefaultTrueRecursively,