Hi,

this avoids the need to use -fno-threadsafe-statics on
arm-none-eabi or working around that problem by supplying
a dummy __sync_synchronize function which might
just lead to silent code failure of the worst kind
(non-reproducable, racy) at runtime, as was pointed out
on previous discussions here.

When the atomic access involves a call to __sync_synchronize
it is better to call __cxa_guard_acquire unconditionally,
since it handles the atomics too, or is a non-threaded
implementation when there is no gthread support for this target.

This fixes also a bug for the ARM EABI big-endian target,
that is, previously the wrong bit was checked.


Regression tested successfully on arm-none-eabi with newlib-3.3.0.

Is it OK for trunk?


Thanks
Bernd.