Exporting G-code on a worker thread did not work correctly as the worker
threads were using user's locale, not "C" locale.
The "C" locale is newly enforced to TBB worker threads by
name_tbb_thread_pool_threads_set_locale()
These new API functions are not available on Windows 7 and on older Windows 10,
thus they are newly loaded dynamically and the functions using it retur
a bool indicating whether the functionality is supported or not.
Also the OSX variants that are not supported newly return false instead
of throwing an exception.
Fixes#4972#4974
The following threads are named with this commit:
slic3r_main, slic3r_BackgroundSlicingProcess,
slic3r_tbbpool_xx_yy where xx is a one based index of the TTB thread
and yy is the platform thread ID.
