Add "aidl.flags:" property for cc_/java_ modules

The property can be used to pass additional flags to the AIDL compiler.
For example,

  cc_library {
    ..
    srcs: ["Foo.aidl"],
    aidl: {
      flags: [
        "-Werror",      // warnings as error
        "-Weverything", // turn on all warnings
      ],
    },
  }

Bug: 168028537
Test: soong test
Change-Id: I8120eeae7cd7b1acdd34c554af996a29e760a368

cc/cc_test.go

@@ -4244,3 +4244,21 @@ func TestStubsLibReexportsHeaders(t *testing.T) {
 		t.Errorf("expected %q in cflags, got %q", "-Iinclude/libbar", cFlags)
 	}
 }
+
+func TestAidlFlagsPassedToTheAidlCompiler(t *testing.T) {
+	ctx := testCc(t, `
+		cc_library {
+			name: "libfoo",
+			srcs: ["a/Foo.aidl"],
+			aidl: { flags: ["-Werror"], },
+		}
+	`)
+
+	libfoo := ctx.ModuleForTests("libfoo", "android_arm64_armv8-a_static")
+	manifest := android.RuleBuilderSboxProtoForTests(t, libfoo.Output("aidl.sbox.textproto"))
+	aidlCommand := manifest.Commands[0].GetCommand()
+	expectedAidlFlag := "-Werror"
+	if !strings.Contains(aidlCommand, expectedAidlFlag) {
+		t.Errorf("aidl command %q does not contain %q", aidlCommand, expectedAidlFlag)
+	}
+}