*/Android.mk: add a check for NDK_ROOT

This simplifies integration with the Android platform and avoids the
files from being used when a non-NDK build is performed. In that case
Android.bp is preferred.

Change-Id: I6e334cf8b05a19da8452405f5f448f9e4b6e4a40

Android.mk

@@ -1,3 +1,5 @@
+# Ignore this file during non-NDK builds.
+ifdef NDK_ROOT
 LOCAL_PATH := $(call my-dir)
 
 WEBP_CFLAGS := -Wall -DANDROID -DHAVE_MALLOC_H -DHAVE_PTHREAD -DWEBP_USE_THREAD
@@ -289,3 +291,4 @@ include $(WEBP_SRC_PATH)/examples/Android.mk
 ifeq ($(USE_CPUFEATURES),yes)
   $(call import-module,android/cpufeatures)
 endif
+endif  # NDK_ROOT

examples/Android.mk

@@ -1,3 +1,5 @@
+# Ignore this file during non-NDK builds.
+ifdef NDK_ROOT
 LOCAL_PATH := $(call my-dir)
 
 ################################################################################
@@ -91,3 +93,4 @@ LOCAL_STATIC_LIBRARIES := example_util imageio_util webp
 LOCAL_MODULE := webpinfo_example
 
 include $(BUILD_EXECUTABLE)
+endif  # NDK_ROOT

imageio/Android.mk

@@ -1,3 +1,5 @@
+# Ignore this file during non-NDK builds.
+ifdef NDK_ROOT
 LOCAL_PATH := $(call my-dir)
 
 ################################################################################
@@ -52,3 +54,4 @@ LOCAL_STATIC_LIBRARIES := imageio_util
 LOCAL_MODULE := imageenc
 
 include $(BUILD_STATIC_LIBRARY)
+endif  # NDK_ROOT