Auto merge of #798 - vojtechkral:glibc2.26, r=alexcrichton
Auto merge of #798 - vojtechkral:glibc2.26, r=alexcrichton

Fix glibc 2.26 incompatibilities #788

Hopefully the `xlocale.h` → `locale.h` change won't break something else somewhere...

cactorium/libc,rust-lang/libc,rust-lang-nursery/libc,rust-lang/libc,cactorium/libc,rust-lang-nursery/libc,rust-lang/libc,cactorium/libc,rust-lang-nursery/libc