Add some defines for the compiler

src/openvr_api_public.cpp

@@ -17,6 +17,8 @@ using vr::VRInitError_None;
 
 // figure out how to import from the VR API dll
 #if defined(_WIN32)
+#define DYNAMIC_LIB_EXT ".dll"
+#define PROGRAM_EXT ".exe"
 
 #if !defined(OPENVR_BUILD_STATIC)
 #define VR_EXPORT_INTERFACE extern "C" __declspec( dllexport )