[CMake] Android NDK r12 appends ".x" to libgcc dir

The Android NDK r12 release appends a ".x" to the libgcc directory;
it is now:

```
android-ndk-r12/toolchains/arm-linux-androideabi-4.9/prebuilt/linux-x86_64/lib/gcc/arm-linux-androideabi/4.9.x
```

Update the linker path for the Android build to accomodate this change.

Author: modocache

cmake/modules/AddSwift.cmake

@@ -290,7 +290,7 @@ function(_add_variant_link_flags)
   elseif("${LFLAGS_SDK}" STREQUAL "ANDROID")
     list(APPEND result
         "-ldl"
-        "-L${SWIFT_ANDROID_NDK_PATH}/toolchains/arm-linux-androideabi-${SWIFT_ANDROID_NDK_GCC_VERSION}/prebuilt/linux-x86_64/lib/gcc/arm-linux-androideabi/${SWIFT_ANDROID_NDK_GCC_VERSION}"
+        "-L${SWIFT_ANDROID_NDK_PATH}/toolchains/arm-linux-androideabi-${SWIFT_ANDROID_NDK_GCC_VERSION}/prebuilt/linux-x86_64/lib/gcc/arm-linux-androideabi/${SWIFT_ANDROID_NDK_GCC_VERSION}.x"
         "${SWIFT_ANDROID_NDK_PATH}/sources/cxx-stl/llvm-libc++/libs/armeabi-v7a/libc++_shared.so"
         "-L${SWIFT_ANDROID_ICU_UC}" "-L${SWIFT_ANDROID_ICU_I18N}")
   else()