Remove libthread_db from bionic.

The NDK statically links its own copy into gdb.

Bug: 11882807
Change-Id: I0c7ed8761c32df3cc3644258551bc7d2e263f47b

Conflicts:
	libthread_db/libthread_db.c
Fix 32-bit mmap/mmap64 handling of negative offsets.

We don't actually need to worry about sign extension if we reject
negative values ourselves. Previously it was possible to come up
with negative but aligned values that we would pass to the kernel;
in the case of mmap (as opposed to mmap64) we'd incorrectly turn
those into large positive offsets.

Change-Id: I2aa583e0f892d59bb77429aea8730b72db32dcb0

Conflicts:
	libc/bionic/mmap.cpp
	tests/Android.mk