[C++11] More 'nullptr' conversion. In some cases just using a boolean check instead of comparing to nullptr.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206142 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/MachineCodeEmitter.h

@@ -262,7 +262,7 @@ public:
     // Check for buffer overflow.
     if (Size >= (uintptr_t)(BufferEnd-CurBufferPtr)) {
       CurBufferPtr = BufferEnd;
-      Result = 0;
+      Result = nullptr;
     } else {
       // Allocate the space.
       Result = CurBufferPtr;