use ndk-buid for building webp on Android platform

Author: zilongshanren

build/android.ini

@@ -40,7 +40,7 @@ cfg_build_fat_library=no
 
 #whether use mthumb instruction or not
 #format  cfg_${libname}_${archname}_use_mthumb
-cfg_curl_arm_use_mthumb=no
+cfg_curl_arm_use_mthumb=no  #for compile issue
 
 #debug and release mode flag
 cfg_build_release_mode="-O3 -DNDEBUG "

contrib/src/webp/rules.mak

@@ -15,7 +15,14 @@ webp: libwebp-$(WEBP_VERSION).tar.gz .sum-webp
 	$(MOVE)
 
 .webp: webp
+ifdef HAVE_ANDROID
+	cd $< && echo "APP_ABI:=$(MY_TARGET_ARCH)" >> Application.mk
+	cd $< && ln -s $(shell pwd)/webp $(shell pwd)/webp/jni
+	cd $< && ndk-build
+	cd $< && cp obj/local/$(MY_TARGET_ARCH)/libwebp.a $(PREFIX)/lib/
+else
 	cd $< && $(HOSTVARS) ./configure $(HOSTCONF)
 	cd $< && $(MAKE)
 	cd $< && $(MAKE) install
+endif
 	touch $@