also "backport" two glibc fixes:

- ipc_perm.mode is c_uint. [commit][1] [discussion][2]
- bump SIGSTKSZ to 16384. [commit][3] [discussion][4]

so libc-test passes.

[1]: https://sourceware.org/git/?p=glibc.git;a=commit;h=5c40c3bab2
[2]: https://www.sourceware.org/ml/libc-alpha/2014-10/msg00446.html
[3]: https://sourceware.org/git/?p=glibc.git;a=commit;h=b763f6ae859ecea70a5dacb8ad45c71d5f667e2e
[4]: https://sourceware.org/ml/libc-alpha/2015-04/msg00033.html

closes #231