Some versions of GCC replace a struct copy with a call to 'memcpy',
which it is fully in its rights to do. Unfortunately on ARM platforms,
that have no direct calls to memcpy, the optimizer (in the presence
of -fwhole-program) drops the implementation of memcpy, even as it
is outputting calls to it.
Add the USED attribute prevents the optimizer from dropping the
function eagerly.
Create new function "clz" which invokes __builtin_clz
Tell the C parser to not try translate it (DONT_TRANSLATE), but instead
to trust the spec we provide (FNSPEC+MODIFIES).
Squashed the fix by Anna Lyons:
rearrange CLZ in util.h and s/__builtin__clz/__builtin_clz/
