MSL_C header cleanup (#2988)

* msl_c header cleanup

* math header cleanup

* fix rest of shieldD configs

* cleanup cflag configs a bit

* fix shield build

src/d/actor/d_a_obj_lv4digsand.cpp

@@ -9,7 +9,7 @@
 #include "d/d_com_inf_game.h"
 #include "d/actor/d_a_player.h"
 #include "d/d_item.h"
-#include <cmath.h>
+#include <math.h>
 
 void daObjL4DigSand_c::initBaseMtx() {
     mpModel->setBaseScale(scale);