Fix for compiling with clang -std=c11 on Linux.

I don't know if this won't break everything else. It at least compiles for me on Arch Linux with Clang version:

	$ clang --version
	clang version 3.5.0 (tags/RELEASE_350/final)
	Target: x86_64-unknown-linux-gnu
	Thread model: posix

… as well as on Mac OS X v10.9.5 with Clang version:

	$ clang --version
	Apple LLVM version 6.0 (clang-600.0.56) (based on LLVM 3.5svn)
	Target: x86_64-apple-darwin13.4.0
	Thread model: posix