Fix Android toolchain file

This got broken with the new Android SDK update, fix this.

toolchain-android.cmake

@@ -1,22 +1,44 @@
-if("$ENV{ARMv8}") # GCC 4.9
+if(BUILD_64_BIT) # ARMv8 with GCC 4.9
   set(BUILD_ANDROID64 1)
-  set(C_COMPILER aarch64-linux-android)
-  set(CXX_COMPILER aarch64-linux-android)
-  set(IDENTIFIER -4.9-aarch64)
-else() # GCC 4.8  
-  set(BUILD_ANDROID 1)
+  set(ANDROID_NDK_TOOL_PREFIX aarch64-linux-android)
+  set(_ndk_suffix -4.9-aarch64)
+else() # GCC 4.8
   set(ARM_TARGET "armeabi-v7a")
-  set(C_COMPILER arm-linux-androideabi)
-  set(CXX_COMPILER arm-linux-androideabi)
+  set(ANDROID_NDK_TOOL_PREFIX arm-linux-androideabi)
 endif()
+set(BUILD_ANDROID 1)
 set(CMAKE_SYSTEM_NAME Linux)
 set(CMAKE_SYSTEM_PROCESSOR arm)
 set(CMAKE_SYSTEM_VERSION 1)
 set(BUILD_ARM 1)
-set(LOCAL_ARM_NEON "true")
-set(ANDROID_COMMON_FLAGS " --sysroot=${LLVM_ANDROID_TOOLCHAIN_DIR}${IDENTIFIER}/sysroot -B${LLVM_ANDROID_TOOLCHAIN_DIR}${IDENTIFIER} ")
-set(CMAKE_C_COMPILER ${LLVM_ANDROID_TOOLCHAIN_DIR}${IDENTIFIER}/bin/${C_COMPILER}-gcc)
-set(CMAKE_CXX_COMPILER ${LLVM_ANDROID_TOOLCHAIN_DIR}${IDENTIFIER}/bin/${CXX_COMPILER}-g++)
+
+if(MSYS)
+  set(_exe_suffix .exe)
+endif()
+
+#For reasons beyond my comprehension, this file is parsed multiple times
+#and in some of them, cache variables are not preserved so we have to store
+#this in an environmental variable...
+if(NOT LLVM_ANDROID_TOOLCHAIN_DIR)
+  set(LLVM_ANDROID_TOOLCHAIN_DIR $ENV{LLVM_ANDROID_TOOLCHAIN_DIR})
+else()
+  set(ENV{LLVM_ANDROID_TOOLCHAIN_DIR} ${LLVM_ANDROID_TOOLCHAIN_DIR} CACHE PATH)
+endif()
+
+find_path(ANDROID_NDK_ROOT bin/${ANDROID_NDK_TOOL_PREFIX}-gcc${_exe_suffix} PATHS
+  ${LLVM_ANDROID_TOOLCHAIN_DIR}${_ndk_suffix} #legacy variable
+  /opt/android-standalone-toolchain${_ndk_suffix}
+  ${LLVM_ANDROID_TOOLCHAIN_DIR}
+  /opt/android-standalone-toolchain
+)
+if(NOT ANDROID_NDK_ROOT)
+  message(FATAL_ERROR "ANDROID_NDK_ROOT could not be located. Have you installed the NDK?")
+endif()
+
+set(ANDROID_COMMON_FLAGS " --sysroot=${ANDROID_NDK_ROOT}/sysroot -B${ANDROID_NDK_ROOT} ")
+set(CMAKE_C_COMPILER ${ANDROID_NDK_ROOT}/bin/${ANDROID_NDK_TOOL_PREFIX}-gcc${_exe_suffix} CACHE FILEPATH "C Compiler" FORCE)
+set(CMAKE_CXX_COMPILER ${ANDROID_NDK_ROOT}/bin/${ANDROID_NDK_TOOL_PREFIX}-g++${_exe_suffix} CACHE FILEPATH "C++ Compiler" FORCE)
+set(ANDROID_STRIP_COMMAND ${ANDROID_NDK_ROOT}/bin/${ANDROID_NDK_TOOL_PREFIX}-strip)
 set(CMAKE_C_FLAGS "${ANDROID_COMMON_FLAGS}" CACHE STRING "toolchain_cflags" FORCE)
 set(CMAKE_CXX_FLAGS "${ANDROID_COMMON_FLAGS}" CACHE STRING "toolchain_cxxflags" FORCE)
 set(CMAKE_LINK_FLAGS "${ANDROID_COMMON_FLAGS}" CACHE STRING "toolchain_linkflags" FORCE)