[Toybox] NDK r18 build.

[Rob Landley]

I downloaded the release 18 NDK and installed it:

  sudo build/tools/make_standalone_toolchain.py --arch x86_64 --api 28 \
    --install-dir /opt/android/x86_64

Then in order to build:

  export CROSS_COMPILE=/opt/android/x86_64/bin/llvm- LDFLAGS=--static
  make distclean
  make defconfig
  make

I need to:

  A) add the llvm-cc symlink to clang.

  B) disable the android logger because liblog.so doesn't have a
     corresponding liblog.a.

(I'm trying to move compile time probes into portability.h but that can't
distinguish between static and non-static linking. But needing to pass the same
flags to defconfig and the the actual compile is kinda awkward/brittle too...)

Rob