clang-modernize -use-nullptr

and s/\bNULL\b/nullptr/g for *.cpp/h/mm files not compiled on my machine

Source/Core/VideoCommon/PerfQueryBase.cpp

@@ -1,7 +1,7 @@
 #include "VideoCommon/PerfQueryBase.h"
 #include "VideoCommon/VideoConfig.h"
 
-PerfQueryBase* g_perf_query = 0;
+PerfQueryBase* g_perf_query = nullptr;
 
 bool PerfQueryBase::ShouldEmulate()
 {