Butmp android api to 24

Makefile

diff --git a/Makefile b/Makefile
index 5259b81..868cc49 100644
--- a/Makefile
+++ b/Makefile
@@ -157,20 +157,20 @@
 
 ifeq ($(ANDROID_CLANG),true)
   # clang works only for APIs >= 23, so default to it if not set
-  ANDROID_API ?= android-23
+  ANDROID_API ?= android-24
   ifeq ($(ANDROID_APP_ABI),armeabi-v7a)
-    ANDROID_NDK_TOOLCHAIN ?= arm-linux-androideabi-clang3.6
+    ANDROID_NDK_TOOLCHAIN ?= arm-linux-androideabi-4.9
   else ifeq ($(ANDROID_APP_ABI),x86)
-    ANDROID_NDK_TOOLCHAIN ?= x86-clang3.6
+    ANDROID_NDK_TOOLCHAIN ?= x86-clang
   else ifeq ($(ANDROID_APP_ABI),arm64-v8a)
-    ANDROID_NDK_TOOLCHAIN ?= aarch64-linux-android-clang3.6
+    ANDROID_NDK_TOOLCHAIN ?= aarch64-linux-android-clang
   else ifeq ($(ANDROID_APP_ABI),x86_64)
-    ANDROID_NDK_TOOLCHAIN ?= x86_64-clang3.6
+    ANDROID_NDK_TOOLCHAIN ?= x86_64-clang
   else
     $(error Unsuported / Unknown APP_API '$(ANDROID_APP_ABI)')
   endif
 else
-  ANDROID_API           ?= android-21
+  ANDROID_API           ?= android-24
   ANDROID_NDK_TOOLCHAIN ?=
 endif