Correctly align the stack. The early csu assumed we passed the aux vector
in through the stack pointer, however this may have been misaligned
causing some userland applications to crash. A workaround was committed in
r284707 where userland would check if the aux vector was passed using the
old or new ABI and adjust the stack if needed. As 4 months have passed it
is time to move to the new ABI, with the expectation the compat code in csu
and the runtime linker to be removed in the future.

Sponsored by: ABT Systems Ltd