source-highlight: Don't do a parallel build

The "make check" appears to have a race condition.

http://hydra.nixos.org/build/7116409
glibc: Apply upstream patch for scanf regression

https://sourceware.org/bugzilla/show_bug.cgi?id=15917

This broke Atlas.

http://hydra.nixos.org/build/7072399
http://sourceforge.net/p/math-atlas/discussion/75123/thread/dc45bb67/