Sections and TLS support for Android executables

This is the remaining piece to build druntime for Android/x86, along with a corrected function declaration in sys/time.d.  All 39 druntime modules' unit tests consistently pass on Android/x86 with this patch, though `core.sync.semaphore` throws an `InvalidMemoryOperation` exception even though its tests pass.  I uncommented `FD_CLR` and friends when running the tests: I'll verify that and add it to this pull later.  Finally, I built everything with `-fPIC`, since that's how Android does it and we'll need it to build shared libraries for Android apps/apks later.

This pull depends on packed TLS for ELF working on dmd, [here's that patch](http://164.138.25.188/dmd/packed_tls_for_elf.patch).  This pull isn't finished yet, just putting it up so others can use it in the meantime.  I'll make the tweaks mentioned and it should be ready for merging then.