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/ScreenGameplay.cpp

@@ -61,6 +61,8 @@
 #include "Profile.h" // for replay data stuff
 #include "RageDisplay.h"
 
+#include <cmath>
+
 // Defines
 #define SHOW_LIFE_METER_FOR_DISABLED_PLAYERS	THEME->GetMetricB(m_sName,"ShowLifeMeterForDisabledPlayers")
 #define SHOW_SCORE_IN_RAVE			THEME->GetMetricB(m_sName,"ShowScoreInRave")
@@ -1701,7 +1703,7 @@ void ScreenGameplay::Update( float fDeltaTime )
 			fSpeed *= GetHasteRate();
 
 		RageSoundParams p = m_pSoundMusic->GetParams();
-		if( fabsf(p.m_fSpeed - fSpeed) > 0.01f && fSpeed >= 0.0f)
+		if( std::abs(p.m_fSpeed - fSpeed) > 0.01f && fSpeed >= 0.0f)
 		{
 			p.m_fSpeed = fSpeed;
 			m_pSoundMusic->SetParams( p );