As discovered building the latest 'fd', the __posix_readdir_r symbol is only available in the Solaris & illumos 32-bit libc. For 32-bit libraries, there is some confusing symbol shuffling that occurs to provide compatibility between traditional Solaris, draft POSIX, and official POSIX behavior for readdir_r (which is where __posix_readdir_r originates).

By the time 64-bit was introduced in Solaris, that was resolved and there is only readdir_r for 64-bit binaries. Since rust (currently) only supports 64-bit targets on Solarish (Solaris & illumos) targets, the symbol renaming in mod.rs is unnecessary.