arm: rewrite crtbegin* as C files.

Rewrite
 crtbegin.S     -> crtbegin.c
 crtbegin_so.S  -> crtbegin_so.c

This change allows us to generate PIC code without relying
on text relocations.

As a consequence of this rewrite, also rewrite
  __dso_handle.S    -> __dso_handle.c
  __dso_handle_so.S -> __dso_handle_so.c
  atexit.S          -> atexit.c

In crtbegin.c _start, place the __PREINIT_ARRAY__, __INIT_ARRAY__,
__FINI_ARRAY__, and __CTOR_LIST__ variables onto the stack, instead of
passing a pointer to the text section of the binary.

This change appears sorta wonky, as I attempted to preserve,
as much as possible, the structure of the original assembly.
As a result, you have C files including other C files, and other
programming uglyness.

Result: This change reduces the number of files with text-relocations
from 315 to 19 on my Android build.

Before:
  $ scanelf -aR $OUT/system | grep TEXTREL | wc -l
  315

After:
  $ scanelf -aR $OUT/system | grep TEXTREL | wc -l
  19

Change-Id: Ib9f98107c0eeabcb606e1ddc7ed7fc4eba01c9c4

Conflicts:
	libc/Android.mk
	libc/arch-arm/bionic/crtbegin.S
	libc/arch-arm/bionic/crtbegin.c
	libc/arch-arm/bionic/crtbegin_dynamic.S
	libc/arch-arm/bionic/crtbegin_so.c

Bug 1056337 - Investigate upgrading the toolchain used for B2G ICS builds (and stop using GCC 4.4)
We need to apply these changes in order to compile with a newer toolchain (because of text relocations in CRT stuff)