How to compile with c11 standard library on OS X with clang?

Hey I am trying to compile c code that uses functions from the c11 standard library on OS X with clang.

The compiler option -std=c11 allows me to use c11 language features. But when I am using new functions like at_quick_exit I get the following warning implicit declaration of function 'at_quick_exit' is invalid in C99.

The source code has the following line #include <stdlib.h> The clang option -stdlib does not help.

My Systems:

OS X Yosemite 10.10.3

$ clang -v
Apple LLVM version 6.1.0 (clang-602.0.53) (based on LLVM 3.6.0svn)
Target: x86_64-apple-darwin14.3.0
Thread model: posix

Ubuntu 14.04 LTS

$ clang -v
Ubuntu clang version 3.4-1ubuntu3 (tags/RELEASE_34/final) (based on LLVM 3.4)
Target: x86_64-pc-linux-gnu 
Thread model: posix

To be more explicit. How can I get on OS X a c11 standard library?

Thanks for any kind of help.