Make LLVM compile on DragonFly BSD (PR2499).

Patch by Hasso Tepper!


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@52781 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/System/Mutex.cpp b/lib/System/Mutex.cpp
index 81dcd3b..f55dd3f 100644
--- a/lib/System/Mutex.cpp
+++ b/lib/System/Mutex.cpp
@@ -75,7 +75,7 @@
     errorcode = pthread_mutexattr_settype(&attr, kind);
     assert(errorcode == 0);
 
-#if !defined(__FreeBSD__) && !defined(__OpenBSD__) && !defined(__NetBSD__)
+#if !defined(__FreeBSD__) && !defined(__OpenBSD__) && !defined(__NetBSD__) && !defined(__DragonFly__)
     // Make it a process local mutex
     errorcode = pthread_mutexattr_setpshared(&attr, PTHREAD_PROCESS_PRIVATE);
 #endif