Fix compilation errors for std=c++2a

Author: mixern6

public/mathlib/mathlib.h

@@ -329,7 +329,7 @@ void inline SinCos( float radians, float *sine, float *cosine )
 		fstp DWORD PTR [eax]
 	}
 #elif defined( GNUC )
-	register double __cosr, __sinr;
+	double __cosr, __sinr;
  	__asm __volatile__ ("fsincos" : "=t" (__cosr), "=u" (__sinr) : "0" (radians));
 
   	*sine = __sinr;
@@ -632,7 +632,9 @@ template <class T> FORCEINLINE T AVG(T a, T b)
 //
 // Returns a clamped value in the range [min, max].
 //
+#if __cplusplus <= 201402L
 #define clamp(val, min, max) (((val) > (max)) ? (max) : (((val) < (min)) ? (min) : (val)))
+#endif
 
 inline float Sign( float x )
 {

public/tier0/threadtools.h

@@ -683,7 +683,7 @@ class CThreadFastMutex
 			return false;
 
 		ThreadMemoryBarrier();
-		++m_depth;
+		m_depth = m_depth + 1;
 		return true;
 	}
 
@@ -744,7 +744,7 @@ class CThreadFastMutex
 			DebuggerBreak();
 #endif
 
-		--m_depth;
+		m_depth = m_depth - 1;
 		if ( !m_depth )
 		{
 			ThreadMemoryBarrier();