Android: Search for NDK and standalone toolchain in more places

Commonly used Android toolchain files that pre-date CMake upstream
support use a few environment and CMake variables as search locations.
Use them too to aid transition.

Modules/Platform/Android-Determine.cmake

@@ -88,8 +88,16 @@ else()
     set(CMAKE_ANDROID_NDK "${_ANDROID_SYSROOT_NDK}")
   elseif(IS_DIRECTORY "${_ANDROID_SYSROOT_STANDALONE_TOOLCHAIN}")
     set(CMAKE_ANDROID_STANDALONE_TOOLCHAIN "${_ANDROID_SYSROOT_STANDALONE_TOOLCHAIN}")
+  elseif(IS_DIRECTORY "${ANDROID_NDK}")
+    file(TO_CMAKE_PATH "${ANDROID_NDK}" CMAKE_ANDROID_NDK)
+  elseif(IS_DIRECTORY "${ANDROID_STANDALONE_TOOLCHAIN}")
+    file(TO_CMAKE_PATH "${ANDROID_STANDALONE_TOOLCHAIN}" CMAKE_ANDROID_STANDALONE_TOOLCHAIN)
   elseif(IS_DIRECTORY "$ENV{ANDROID_NDK_ROOT}")
     file(TO_CMAKE_PATH "$ENV{ANDROID_NDK_ROOT}" CMAKE_ANDROID_NDK)
+  elseif(IS_DIRECTORY "$ENV{ANDROID_NDK}")
+    file(TO_CMAKE_PATH "$ENV{ANDROID_NDK}" CMAKE_ANDROID_NDK)
+  elseif(IS_DIRECTORY "$ENV{ANDROID_STANDALONE_TOOLCHAIN}")
+    file(TO_CMAKE_PATH "$ENV{ANDROID_STANDALONE_TOOLCHAIN}" CMAKE_ANDROID_STANDALONE_TOOLCHAIN)
   endif()
   # TODO: Search harder for the NDK or standalone toolchain.
 endif()