Provide a polyfill over std::to_string

Android apparently does not support `std::to_string`, so we add a
small polyfill over it. Right now only the ULP matcher uses it,
but we have had plans to use it in `StringMaker<int>` and friends,
as it performs a lot better than `std::stringstream` based
stringification on MSVC.

See #1280 for more details

include/internal/catch_matchers_floating.cpp

@@ -6,6 +6,7 @@
  */
 
 #include "catch_matchers_floating.h"
+#include "catch_to_string.hpp"
 #include "catch_tostring.h"
 
 #include <cstdlib>
@@ -115,7 +116,7 @@ namespace Floating {
     }
 
     std::string WithinUlpsMatcher::describe() const {
-        return "is within " + std::to_string(m_ulps) + " ULPs of " + ::Catch::Detail::stringify(m_target) + ((m_type == FloatingPointKind::Float)? "f" : "");
+        return "is within " + Catch::to_string(m_ulps) + " ULPs of " + ::Catch::Detail::stringify(m_target) + ((m_type == FloatingPointKind::Float)? "f" : "");
     }
 
 }// namespace Floating