GCC Toolchain Path Incorrect Post R22 NDK

After R22 of the NDK, the NDK is clang only for build it seems? Per https://github.com/android/ndk/issues/1375 this means that the GCC toolchains that are attempting to be found no longer are (specifically at https://github.com/facebook/buck/blob/5444652af489563ddaf595a634341dd14fd41399/src/com/facebook/buck/android/toolchain/ndk/impl/NdkCxxPlatforms.java#L1250-L1253 this causes error using newer toolchains than R22).