Clang emits aligned AVX stores for things like zeroing stack-allocated
variables when using -mavx even with -fno-tree-vectorize set which can
result in crashes if this occurs before we've realigned the stack.

Previously we only ensured that the stack was realigned before calling
assembly functions that accesses stack-allocated buffers but this is
not sufficient. Fix the issue by changing the stack realignment to
instead occur immediately in all CLI, API and thread entry points.