Fix libcompiler_rt to contain lib/atomic.o, depends on libc/libm, etc

1. lib/atomic.c provides essential functions like __atomic_exchange
   used by intrinsic functions expanded by clang
2. Make libcompiler_rt*so depends on -lc and -lm otherwise whoever
   binary links it may fail to launch due to missing __cxa_atexit, etc.
3. No need to add -minline-thumb1-jumptable for clang, because
   a) first, clang doesn't generate thumb_jumptable helps this flag
      tries to stop, and
   b) clang doesn't understand this flag

Change-Id: I34e9d29492ab47e43c54e82865e4166e6cd117a5
[experimental] test libc++ built by clang; link tests with compiler-rt

Trying to make libc++ work with clang
1. Turns out libc++ needs some features exists in clang to work.  Previously
   we compile all STL in NDK with default compiler which is gcc 4.6.
   In this experiment, we switch to clang3.3 (exists since r9)

   ./build/tools/build-cxx-stl.sh --stl=libc++ --ndk-dir=$NDK --llvm-version=3.3

2. Clang needs compiler-rt for helpers used by code expanded
   from intrinsics (eg. __atomic_exchange).  This patch add -lcompiler_rt*
   for linker.

To test:
  cd $NDK
  ./build/tools/make-standalone-toolchain.sh --platform=android-9 --llvm-version=3.3 \
    --install-dir=/path/to/ndk/standalone/ndk-api9-arm --arch=arm

  cd $NDK/sources/cxx-stl/llvm-libc++/libcxx/test
  PATH=/path/to/ndk/standalone/ndk-api9-arm:$PATH \
    ./testit_android --abi=armeabi-v7a --cxx=arm-linux-androideabi-clang++

Fail count of section/test drop from 208/682 to 90/242 (out of total 1071/4418)

Change-Id: I213448129f82b70542fca4e4603fb50e023a1f9e