[MIPS] Rewrite MIPS crtbegin* as C files.

This updates the MIPS arch to be much more in
sync with the commit Nick Kralevich made last
June; see 9d40326830c2bd407427889c554adeb915ee6b4a.

    Rewrite
     crtbegin.S        -> crtbegin.c
     crtbegin_so.S     -> crtbegin_so.c
     __dso_handle.S    -> __dso_handle.c
     __dso_handle_so.S -> __dso_handle_so.c
     atexit.S          -> atexit.c

Previously __do_global_dtors_aux was in the tasks
__FINI_ARRAY__ linked with crtbegin.S and it now being
removed as there is no need to call a destructor just
before terminating a process.

Shared libraries, on the other hand, are linked with
crtbegin_so.c and have a hidden destructor declared
to allow the bionic linker to call __on_dlclose().

Change-Id: Ieb4da5199b54573de05743990e309db381a11cb8
Signed-off-by: Pete Delaney  <piet.delaney@imgtec.com>
Signed-off-by: Chao-Ying Fu  <chao-ying.fu@imgtec.com>
Signed-off-by: Chris Dearman <chris.dearman@imgtec.com>
Remove some non-unused makefile generality.

MIPS uses .c files like ARM and x86 now.

Change-Id: Ie580647e385121c380316c443ec199dabf657ff8

Conflicts:
	libc/Android.mk
Restore dlmalloc mmap threshold to 64k

Restoring DEFAULT_MMAP_THRESHOLD to 64k, the way it was before
999089181ef60bb67e1a49f2cf6f4ec608a7caf8.

This forces allocations in the 64k-256k range to be mmaped.

Change-Id: Iace55ed638edd272b3e94fa6cd2ddd349042be84
Signed-off-by: Rom Lemarchand <romlem@google.com>
[MIPS] __dso_handle.S and __dso_handle_so.S not needed.

Global hidden variable __dso_handle is now declared in:
       bionic/libc/private/__dso_handle.h

Change-Id: I8e951a8d7c65877bafc1be23a7fff6d44d3a2846
Signed-off-by: Pete Delaney  <piet.delaney@imgtec.com>
Signed-off-by: Chao-Ying Fu  <chao-ying.fu@imgtec.com>