compile fixes for MSVC!

* function must return value!
* missing _USE_MATH_DEFINES for M_PI

intern/ghost/intern/GHOST_SystemWin32.cpp

@@ -1097,10 +1097,10 @@ void GHOST_SystemWin32::putClipboard(GHOST_TInt8 *buffer, bool selection) const
 
 GHOST_TUns8* GHOST_SystemWin32::getSystemDir() const
 {
-
+	return NULL;
 }
 
 GHOST_TUns8* GHOST_SystemWin32::getUserDir() const
 {
-
+	return NULL;
 }

source/blender/blenkernel/intern/unit.c

@@ -24,6 +24,9 @@
 #include <stdio.h>
 #include <ctype.h>
 #include <string.h>
+#ifdef WIN32
+#define _USE_MATH_DEFINES
+#endif
 #include <math.h>
 
 #include "BLI_winstuff.h"