The C11 revision of the C programming language has built-in multi-threading support as most Phoronix readers are now aware. The C11 threads bring standardization to the threading semantics, lightweight inter-thread communication, etc. In place of explicitly relying upon POSIX Threads (pthreads), the C11 threads are now used and backed by a Boost C11 Threads emulation library.
This emulation library abstracts the thread support while supporting pthreads on POSIX platforms and Win32 threads on Microsoft's releases going back to Windows XP.
The commits adding this Boost library and then taking advantage of the C11 Threads abstraction can be found with this Git search. The changes were made across several commits by José Fonseca at VMware.