Merge changes I14b731d3,I734ef7bc,I29cdfe50,I1fe9a43b,I4c53c502, ... into ndk-r12-release

* changes:
  Support logging in standalone toolchain tests.
  Make the standalone toolchain test better.
  Install linker scripts for libc++.
  Test the new standalone toolchain.
  Fix libdir for STL libs.
  chmod a+x the clang wrappers.
  Direct users to new standalone toolchain tool.
  Change our user docs naming to match DAC.