Prevent name clashes with math macros

This replaces the macros in AvrMath.h with template functions when
included from C++. This prevents name clashes with e.g. the `std::min`
function or similar methods or namespace-local functions. For C, this
still uses a macro (lacking templates), but an improved version that
prevents double evaluation of arguments.

This code is based on the ArduinoCore-API repository, which is in the
process of become the single source of all non-architecture-specific
Arduino API code:

    https://github.com/arduino/ArduinoCore-API/blob/master/api/Common.h

There, only `min` and `max` have been replaced by template functions,
but others will probably follow as well:

    arduino/ArduinoCore-API#85

This fixes Arduino-CI#133.

cpp/arduino/AvrMath.h

@@ -1,26 +1,96 @@
 #pragma once
 #include <math.h>
+#include "ArduinoDefines.h"
 
-#define constrain(x,l,h) ((x)<(l)?(l):((x)>(h)?(h):(x)))
-#define map(x,inMin,inMax,outMin,outMax) (((x)-(inMin))*((outMax)-(outMin))/((inMax)-(inMin))+outMin)
-
-#define sq(x) ((x)*(x))
-
-#define radians(deg) ((deg)*DEG_TO_RAD)
-#define degrees(rad) ((rad)*RAD_TO_DEG)
-
-#ifdef abs
-#undef abs
+#ifdef __cplusplus
+  template<class Amt, class Low, class High>
+  auto constrain(const Amt& amt, const Low& low, const High& high) -> decltype(amt < low ? low : (amt > high ? high : amt ))
+  {
+    return (amt < low ? low : (amt > high ? high : amt ));
+  }
+  template<class X, class InMin, class InMax, class OutMin, class OutMax>
+  auto map(const X& x, const InMin& inMin, const InMax& inMax, const OutMin& outMin, const OutMax& outMax)
+   -> decltype((x - inMin) * (outMax - outMin) / (inMax - inMin) + outMin)
+  {
+    return (x - inMin) * (outMax - outMin) / (inMax - inMin) + outMin;
+  }
+  template<class T>
+  auto radians(const T& deg) -> decltype(deg * DEG_TO_RAD)
+  {
+      return deg * DEG_TO_RAD;
+  }
+  template<class T>
+  auto degrees(const T& rad) -> decltype(rad * RAD_TO_DEG)
+  {
+      return rad * RAD_TO_DEG;
+  }
+  template<class T>
+  auto sq(const T& x) -> decltype(x * x)
+  {
+      return x * x;
+  }
+  template<class T>
+  auto abs(const T& x) -> decltype(x > 0 ? x : -x)
+  {
+      return x > 0 ? x : -x;
+  }
+  template<class T, class L>
+  auto min(const T& a, const L& b) -> decltype((b < a) ? b : a)
+  {
+    return (b < a) ? b : a;
+  }
+  template<class T, class L>
+  auto max(const T& a, const L& b) -> decltype((b < a) ? b : a)
+  {
+    return (a < b) ? b : a;
+  }
+#else
+#ifndef constrain
+#define constrain(amt,low,high) \
+   ({ __typeof__ (amt) _amt = (amt); \
+      __typeof__ (low) _low = (low); \
+      __typeof__ (high) _high = (high); \
+      (amt < low ? low : (amt > high ? high : amt )); })
 #endif
-#define abs(x) ((x)>0?(x):-(x))
-
-#ifdef max
-#undef max
+#ifndef map
+#define map(x,inMin,inMax,outMin,outMax) \
+   ({ __typeof__ (x) _x = (x); \
+       __typeof__ (inMin) _inMin = (inMin); \
+      __typeof__ (inMax) _inMax = (inMax); \
+      __typeof__ (outMin) _outMin = (outMin); \
+      __typeof__ (outMax) _outMax = (outMax); \
+      (_x - _inMin) * (_outMax - _outMin) / (_inMax - _inMin) + _outMin; })
+#endif
+#ifndef radians
+#define radians(deg) \
+   ({ __typeof__ (deg) _deg = (deg); \
+      _deg * DEG_TO_RAD; })
+#endif
+#ifndef degrees
+#define degrees(rad) \
+   ({ __typeof__ (rad) _rad = (rad); \
+      _rad * RAD_TO_DEG; })
+#endif
+#ifndef sq
+#define sq(x) \
+   ({ __typeof__ (x) _x = (x); \
+      _x * _x; })
+#endif
+#ifndef abs
+#define abs(x) \
+   ({ __typeof__ (x) _x = (x); \
+      _x > 0 ? _x : -_x; })
+#endif
+#ifndef min
+#define min(a,b) \
+   ({ __typeof__ (a) _a = (a); \
+      __typeof__ (b) _b = (b); \
+      _a < _b ? _a : _b; })
+#endif
+#ifndef max
+#define max(a,b) \
+   ({ __typeof__ (a) _a = (a); \
+      __typeof__ (b) _b = (b); \
+      _a > _b ? _a : _b; })
 #endif
-#define max(a,b) ((a)>(b)?(a):(b))
-
-#ifdef min
-#undef min
 #endif
-#define min(a,b) ((a)<(b)?(a):(b))
-