FreeBSD does not define pthread_mutexattr_setpshared:
gmake[1]: Entering directory `/usr/home/jeffc/llvm/obj/lib/System'
llvm[1]: Compiling Mutex.cpp for Release build
/usr/home/jeffc/llvm/obj/../lib/System/Mutex.cpp:42: warning: the address of `int llvm::pthread_mutex_init(llvm::pthread_mutex**, llvm::pthread_mutex_attr* const*)', will always evaluate as `true'
/usr/home/jeffc/llvm/obj/../lib/System/Mutex.cpp: In constructor `llvm::sys::Mutex::Mutex(bool)':
/usr/home/jeffc/llvm/obj/../lib/System/Mutex.cpp:66: error: `pthread_mutexattr_setpshared' undeclared (first use this function)
/usr/home/jeffc/llvm/obj/../lib/System/Mutex.cpp:66: error: (Each undeclared identifier is reported only once for each function it appears in.)
gmake[1]: *** [/usr/home/jeffc/llvm/obj/lib/System/Release/Mutex.o] Error 1