avoid clashing definition of round

only enabled if targeting C or a C++ version older than c++17, as it's
assumed that it works in those cases (Arduino targets c++14)

teensy4/wiring.h

 #define typeof(a) decltype(a)
 #endif
 
+#if !defined(__cplusplus) || __cplusplus < 201703L
 #define abs(x) ({ \
   typeof(x) _x = (x); \
   (_x > 0) ? _x : -_x; \
 })
+#define round(x) ({ \
+  typeof(x) _x = (x); \
+  (_x>=0) ? (long)(_x+0.5) : (long)(_x-0.5); \
+})
+#endif /* __cplusplus < 201703L */
+
 #define constrain(amt, low, high) ({ \
   typeof(amt) _amt = (amt); \
   typeof(low) _low = (low); \
   typeof(high) _high = (high); \
   (_amt < _low) ? _low : ((_amt > _high) ? _high : _amt); \
 })
-#define round(x) ({ \
-  typeof(x) _x = (x); \
-  (_x>=0) ? (long)(_x+0.5) : (long)(_x-0.5); \
-})
 #define radians(deg) ((deg)*DEG_TO_RAD)
 #define degrees(rad) ((rad)*RAD_TO_DEG)
 #define sq(x) ({ \