MSVC: Show compiler version in AboutDialog

Make AboutDialog support MSVC compiler info so we can use a screenshot of
it to brag with on #devtalk

include/versioninfo.h

@@ -1,7 +1,11 @@
+#include "lmms_basics.h"
+
 #ifdef __GNUC__
-#define GCC_VERSION "GCC " __VERSION__
+#define COMPILER_VERSION "GCC " __VERSION__
+#elif defined(_MSC_VER)
+#define COMPILER_VERSION "MSVC " STRINGIFY(_MSC_FULL_VER)
 #else
-#define GCC_VERSION "unknown compiler"
+#define COMPILER_VERSION "unknown compiler"
 #endif
 
 #ifdef LMMS_HOST_X86