Pass LLVM_ANDROID_TOOLCHAIN_DIR if set.

This lets one build ASan runtime for ARM/Android by running
make -C tools/clang/runtime/ \
  LLVM_ANDROID_TOOLCHAIN_DIR=/path/to/ndk/toolchain
in an existing build tree.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@166560 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed