ndk: Remove prebuilt C runtime objects. Add sources instead.

This patch removes all prebuilt C runtime object files from
the ndk/platforms/ directory. We replace them with equivalent
assembly sources lifted from the following directories:

  bionic/libc/private/      (for __dso_handle.S and __dso_handle_so.S)
  bionic/libc/arch-$ARCH/   (for all others)

Note: This requires that your NDK's gen-platforms.sh script be
      capable of rebuilding the object files from sources.
      See https://android-review.googlesource.com/36822

The goal here is to make it much easier to update these files,
and track their changes relative to the content of bionic/lib.
For example to fix the following issues in the future:

Change-Id: If4c84e2584b0e58ca3585b034bb8a13a8add8ab9
http://code.google.com/p/android/issues/detail?id=26911
http://code.google.com/p/android/issues/detail?id=23203
34 files changed