Fix ambiguity between clamp implementations

There is an ambiguity between global and std clamp implementations when compiling in c++17,
and on certain toolchains that are not strictly conforming to c++11.
This is solved by putting our clamp implementation in a namespace.

closes https://github.com/official-stockfish/Stockfish/pull/2572

No functional change.

src/misc.h

@@ -64,6 +64,14 @@ std::ostream& operator<<(std::ostream&, SyncCout);
 #define sync_cout std::cout << IO_LOCK
 #define sync_endl std::endl << IO_UNLOCK
 
+namespace Utility {
+
+/// Clamp a value between lo and hi. Available in c++17.
+template<class T> constexpr const T& clamp(const T& v, const T& lo, const T& hi) {
+  return v < lo ? lo : v > hi ? hi : v;
+}
+
+}
 
 /// xorshift64star Pseudo-Random Number Generator
 /// This class is based on original code written and dedicated