DrMi#1899: properly align initial stack
DrMi#1899: properly align initial stack

The latest early injection init changes broke stack alignment, which
results in a crash when using clang (which does not support the old ABI of
not aligning the stack).

Review-URL: https://codereview.appspot.com/304750043

AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio