some libc solaris definitions are not correct

[binarycrusader]

There are a few somewhat subtle errors in the definitions found in src/unix/solaris/mod.rs.

1. pthread_t should be a c_uint, not a uintptr_t just as pthread_key_t is defined
2. fd_set is actually a long on Solaris, so needs to change definition based on target_pointer_width; not only is this only working by chance right now, it prevents process spawning from working correctly on sparc since the 32-bit value is placed in the lower half of the 64-bit value passed to select/pselect
3. for lp64, FD_SETSIZE should actually be 65536 as has been true since 1997

I will send a pull request shortly with proposed fixes. This is the first time I've sent a pull request, so please let me know if I've missed any steps (I've tried to follow the instructions at https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#pull-requests).

/cc @dhduvall