KNOWN ABI BUGS
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time_t is 32-bit. http://b/5819737
off_t is 32-bit. There is off64_t, but no _FILE_OFFSET_BITS support.
sigset_t is too small on ARM and x86 (but correct on MIPS), so support
for real-time signals is broken. http://b/5828899
Too few TLS slots mean we can't allocate 128 pthread_key_t instances,
which POSIX says should be the minimum.
atexit(3) handlers registered by a shared library aren't called on
dlclose(3); this only affects ARM. http://b/4998315