Fix an error in the ABI in rtld_bind_start(). When passing arguments to a

Fix an error in the ABI in rtld_bind_start(). When passing arguments to a
C function, the caller's stack frame must have room to store all of the
arguments to that function. While here, fix stack frame alignment issues.

Without this change, the compiler will save r3 and r4 into the caller's
stack frame before calling setjmp() in _rtld_bind(). These would then
overwrite arguments to the newly-bound function, causing eventual failures.