* non-process-shared POSIX semaphores aren't supported on
Darwin, we use the dispatch framework
* dlsym segfaults with RTLD_NEXT from JIT code, so we must not
even try this for -run. So we need to know in __bound_init
if called from -run code, or from normal code, which means passing
this down also from __bt_init and hence from the stub added in
tcc_add_btstub
* Darwin uses different structures for <ctype.h> facilities, this
merely adds a warning about this
* __libc_freeres doesn't exist
* for non -run modus the context (.prog_base member) is constructed
incorrectly (uses symbol zero for trying to get at the load bias,
which doesn't really work that way), on Mach-O this errors out
(and could also error out on ELF). For now deactivate this, which
makes backtraces not be symbolic on MacOS for not -run.
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