Fix a major typo.

Nicolas, this is probably the cause of the failures you were seeing.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@73770 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/System/Mutex.h

@@ -89,7 +89,7 @@ namespace llvm
       explicit SmartMutex(bool recursive = true) : MutexImpl(recursive) { }
       
       bool acquire() {
-        if (!mt_only && llvm_is_multithreaded())
+        if (!mt_only || llvm_is_multithreaded())
           return MutexImpl::acquire();
         return true;
       }