Turn FIXED_TO_FLOAT into a function

Turn FIXED_TO_FLOAT and FLOAT_TO_FIXED into the functions FixedToFloat and FloatToFixed, though keep the old macros for backwards compatibility. This fixes issues in !861 (merged) and makes !867 (closed) obsolete.

This really has no gameplay implications at all, this is just coding cleanup.

src/m_fixed.h

@@ -38,8 +38,20 @@ typedef INT32 fixed_t;
 /*!
   \brief convert fixed_t into floating number
 */
-#define FIXED_TO_FLOAT(x) (((float)(x)) / ((float)FRACUNIT))
-#define FLOAT_TO_FIXED(f) (fixed_t)((f) * ((float)FRACUNIT))
+
+FUNCMATH FUNCINLINE static ATTRINLINE float FixedToFloat(fixed_t x)
+{
+	return x / (float)FRACUNIT;
+}
+
+FUNCMATH FUNCINLINE static ATTRINLINE fixed_t FloatToFixed(float f)
+{
+	return (fixed_t)(f * FRACUNIT);
+}
+
+// for backwards compat
+#define FIXED_TO_FLOAT(x) FixedToFloat(x) // (((float)(x)) / ((float)FRACUNIT))
+#define FLOAT_TO_FIXED(f) FloatToFixed(f) // (fixed_t)((f) * ((float)FRACUNIT))
 
 
 #if defined (__WATCOMC__) && FRACBITS == 16