Implement blm and bls using an inline loop.

Implement blm and bls using an inline loop.

This replaces a call to memmove() in libc.  That was working for me,
but it can fail because EM programs don't always link to libc.

blm and bls only need to copy aligned words.  They don't need to copy
bytes, and they don't need to copy between overlapping buffers, as
memmove() does.  So the new loop is simpler than memmove().