Clean up math functions

- Remove checking for standard functions from the build system
- Prefix all invocations with std::
- Replace suffixed functions with unprefixed versions
- Include <cmath> in all files that use it and remove the global include

e.g. floorf(x) -> std::floor(x)

src/ScreenContinue.cpp

@@ -8,6 +8,8 @@
 #include "MenuTimer.h"
 #include "MemoryCardManager.h"
 
+#include <cmath>
+
 
 REGISTER_SCREEN_CLASS( ScreenContinue );
 
@@ -25,7 +27,7 @@ void ScreenContinue::BeginScreen()
 	GAMESTATE->SetCurrentStyle( nullptr, PLAYER_INVALID );
 
 	// Unjoin human players with 0 stages left and reset non-human players.
-	// We need to reset non-human players because data in non-human (CPU) 
+	// We need to reset non-human players because data in non-human (CPU)
 	// players will be filled, and there may be stale pointers to things like
 	// edit Steps.
 	FOREACH_ENUM( PlayerNumber, p )
@@ -69,7 +71,7 @@ bool ScreenContinue::Input( const InputEventPlus &input )
 			case GAME_BUTTON_LEFT:
 			case GAME_BUTTON_RIGHT:
 			{
-				float fSeconds = floorf(m_MenuTimer->GetSeconds()) - 0.0001f;
+				float fSeconds = std::floor(m_MenuTimer->GetSeconds()) - 0.0001f;
 				fSeconds = std::max( fSeconds, 0.0001f ); // don't set to 0
 				m_MenuTimer->SetSeconds( fSeconds );
 				Message msg("HurryTimer");
@@ -123,7 +125,7 @@ void ScreenContinue::HandleMessage( const Message &msg )
 /*
  * (c) 2004 Chris Danford
  * All rights reserved.
- * 
+ *
  * Permission is hereby granted, free of charge, to any person obtaining a
  * copy of this software and associated documentation files (the
  * "Software"), to deal in the Software without restriction, including
@@ -133,7 +135,7 @@ void ScreenContinue::HandleMessage( const Message &msg )
  * copyright notice(s) and this permission notice appear in all copies of
  * the Software and that both the above copyright notice(s) and this
  * permission notice appear in supporting documentation.
- * 
+ *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
  * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT OF