Android: Removed custom toolchain file

This commit drops the previous custom CMake toolchain file for Android
in favor of CMake's new built-in toolchain for this (CMake >3.7.2).

This makes building SFML for Android a lot simpler and more straight
forward, working almost as smooth as other platforms.

To configure your build directory, all you have to do is defining just a
few variables the first time you invoke CMake.

**Required Variables**

* `CMAKE_SYSTEM_NAME` must be `Android`, so CMake knows we actually want
  to cross-compile.
* `CMAKE_ANDROID_NDK` must point to the NDK's installation directory,
  e.g. `/usr/android/ndk` or `c:/android/ndk`.

**Recommended Variables**
* `CMAKE_ANDROID_STL_TYPE` defines the STL implementation to be used.
  You should use `c++_shared`, although others might work.

**Optional Variables**
* `CMAKE_SYSTEM_VERSION` can be set to pick a specific SDK version other
  than the latest.
* `CMAKE_ANDROID_ARCH_ABI` defines the target architecture and ABI, for
  example `armeabi` or `armeabi-v7a`.

Based on your system, you might want to enforce a specific generator to
prevent issues, e.g. using `MinGW Makefiles`.

src/SFML/Audio/CMakeLists.txt

@@ -66,7 +66,7 @@ elseif(SFML_OS_ANDROID)
 endif()
 
 # find external libraries
-if(SFML_OS_ANDROID OR SFML_OS_IOS)
+if(SFML_OS_IOS)
     if(NOT SFML_OS_IOS)
         find_host_package(OpenAL REQUIRED)
     endif()

src/SFML/CMakeLists.txt

@@ -36,7 +36,7 @@ elseif(SFML_OS_IOS)
     set(CMAKE_LIBRARY_PATH ${CMAKE_LIBRARY_PATH} "${PROJECT_SOURCE_DIR}/extlibs/libs-ios/")
 elseif(SFML_OS_ANDROID)
     set(CMAKE_INCLUDE_PATH ${CMAKE_INCLUDE_PATH} "${PROJECT_SOURCE_DIR}/extlibs/headers")
-    set(CMAKE_LIBRARY_PATH ${CMAKE_LIBRARY_PATH} "${PROJECT_SOURCE_DIR}/extlibs/libs-android/${ANDROID_ABI}")
+    set(CMAKE_LIBRARY_PATH ${CMAKE_LIBRARY_PATH} "${PROJECT_SOURCE_DIR}/extlibs/libs-android/${CMAKE_ANDROID_ARCH_ABI}")
 endif()
 
 # add the SFML sources path

src/SFML/Graphics/CMakeLists.txt

@@ -116,7 +116,7 @@ if(SFML_OPENGL_ES AND SFML_OS_LINUX)
     find_package(GLES REQUIRED)
     include_directories(${EGL_INCLUDE_DIR} ${GLES_INCLUDE_DIR})
 endif()
-if(SFML_OS_ANDROID OR SFML_OS_IOS)
+if(SFML_OS_IOS)
     find_host_package(Freetype REQUIRED)
 else()
     find_package(Freetype REQUIRED)

src/SFML/Main/SFMLActivity.cpp

@@ -30,6 +30,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <jni.h>
+#include <string>
 
 #define LOGE(...) ((void)__android_log_print(ANDROID_LOG_INFO, "sfml-activity", __VA_ARGS__))