Add entrypoint to build test

Just for convenience, nothing special here

native/build.gradle

@@ -12,7 +12,7 @@ android {
         externalNativeBuild {
             ndkBuild {
                 // Pass arguments to ndk-build.
-                arguments('B_MAGISK=1', 'B_INIT64=1', 'B_BOOT=1',
+                arguments('B_MAGISK=1', 'B_INIT64=1', 'B_BOOT=1', 'B_TEST=1',
                         'MAGISK_DEBUG=1', 'MAGISK_VERSION=debug', 'MAGISK_VER_CODE=INT_MAX')
             }
         }

native/jni/.gitignore

@@ -0,0 +1 @@
+test.cpp

native/jni/Android.mk

@@ -121,6 +121,19 @@ include $(BUILD_EXECUTABLE)
 
 endif
 
+ifdef B_TEST
+
+include $(CLEAR_VARS)
+LOCAL_MODULE := test
+LOCAL_STATIC_LIBRARIES := libutils
+LOCAL_C_INCLUDES := \
+	jni/include \
+	$(LIBUTILS)
+LOCAL_SRC_FILES := test.cpp
+include $(BUILD_EXECUTABLE)
+
+endif
+
 ifdef B_BB
 
 include jni/external/busybox/Android.mk