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

CMakeLists.txt

@@ -187,6 +187,7 @@ set(INTERNAL_HEADERS
         ${HEADER_DIR}/internal/catch_test_spec_parser.h
         ${HEADER_DIR}/internal/catch_text.h
         ${HEADER_DIR}/internal/catch_timer.h
+        ${HEADER_DIR}/internal/catch_to_string.hpp
         ${HEADER_DIR}/internal/catch_tostring.h
         ${HEADER_DIR}/internal/catch_totals.h
         ${HEADER_DIR}/internal/catch_uncaught_exceptions.h