Fix Windows build

Issue: `byte` C++ type was defined several times by different includes, and is also a standard type since C++17
Cause: ninja-build/ninja#1861
Solution: moving `#include common/darktable.h`, which includes `common/win.h` which includes `win/win.h` before `using namespace std` in C++ files.

Thanks to @OlliWa !

src/common/exif.cc

@@ -50,8 +50,6 @@
 
 #include <pugixml.hpp>
 
-using namespace std;
-
 extern "C" {
 #include "common/colorlabels.h"
 #include "common/darktable.h"
@@ -76,6 +74,8 @@ extern "C" {
 #include "develop/masks.h"
 }
 
+using namespace std;
+
 #define DT_XMP_EXIF_VERSION 5
 
 #if EXIV2_TEST_VERSION(0,28,0)