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/RageSoundReader_Chain.cpp

@@ -9,6 +9,8 @@
 #include "RageSoundMixBuffer.h"
 #include "RageSoundUtil.h"
 
+#include <cmath>
+
 
 /*
  * Keyed sounds should pass this object to SoundReader_Preload, to preprocess it.
@@ -53,7 +55,7 @@ void RageSoundReader_Chain::AddSound( int iIndex, float fOffsetSecs, float fPan
 
 	Sound s;
 	s.iIndex = iIndex;
-	s.iOffsetMS = lrintf( fOffsetSecs * 1000 );
+	s.iOffsetMS = std::lrint( fOffsetSecs * 1000 );
 	s.fPan = fPan;
 	s.pSound = nullptr;
 	m_aSounds.push_back( s );
@@ -85,7 +87,7 @@ int RageSoundReader_Chain::LoadSound( RString sPath )
 	}
 
 	m_apNamedSounds[sPath] = pReader;
-	
+
 	m_apLoadedSounds.push_back( m_apNamedSounds[sPath] );
 	return m_apLoadedSounds.size()-1;
 }