sys/cdefs.h: Remove old arm acle-compat.h workaround

The ACLE defines the modern ARM compiler symbols. ARM published
acle-compat.h to ease the transition to the new standard. This standard
is in all modern versions of gcc and clang, only gcc prior to 4.4 lacked
them (though our 4.2.1 back-ported them, IIRC). Since this is no longer
needed, remove the global inclusion in sys/ctypes.h. We should likely
remove arm/include/acle-compat.h as well (it's unused now in the tree),
but I'll make sure this change is the NOP I think it is before moving
ahead there. I also recall at one time some out of tree code needing
this file, though the need for it to make things right has long since
past.

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