Update Makefile

src/Makefile

@@ -165,7 +165,7 @@ ifeq ($(PLATFORM),PLATFORM_ANDROID)
     # Android required path variables
     # NOTE: Starting with Android NDK r21, no more toolchain generation is required, NDK is the toolchain on itself
     ifeq ($(OS),Windows_NT)
-        ANDROID_NDK = C:/android-ndk
+        ANDROID_NDK ?= C:/android-ndk
         ANDROID_TOOLCHAIN = $(ANDROID_NDK)/toolchains/llvm/prebuilt/windows-x86_64
     else
         ANDROID_NDK ?= /usr/lib/android/ndk