Reduce math library code size by 3.4KB (#21575)

Marlin/src/core/macros.h

@@ -112,6 +112,9 @@
 #define SIGN(a) ({__typeof__(a) _a = (a); (_a>0)-(_a<0);})
 #define IS_POWER_OF_2(x) ((x) && !((x) & ((x) - 1)))
 
+#define MFNAN 999999.0f
+#define ISNAN(V) ((V) == MFNAN)
+
 // Macros to constrain values
 #ifdef __cplusplus