While POSIX.1-2001 says that pthread_t is allowed to be
"non-arithmetic", earlier revisions did not allow it, and
many things still assume the original rule and either
complain loudly or fail completely if pthread_t is a struct.
In glibc, pthread_t is typedef'd to 'unsigned long int', but
in musl, it is a pointer type to an opaque struct. We'll go
with the latter option here.
Note that while this breaks ABI combatibility for the libc,
nothing in the x86-64 or aarch64 package repositories uses
pthreads, so this probably doesn't matter too much. If you
are one of the handful of souls brave enough to be maintaining
your own downstream software for ToaruOS and you use pthreads,
it's time to rebuild.
This is an initial change that will be followed up with more
thorough internal changes to our pthreads implementation.
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