Revert "Fix #167"

This reverts commit ef10e7c5dd.

peglib.h

@@ -13,6 +13,9 @@
 #include <cctype>
 #if __has_include(<charconv>)
 #include <charconv>
+#define CPPPEGLIB_HAS_CHARCONV true
+#else
+#define CPPPEGLIB_HAS_CHARCONV false
 #endif
 #include <cstring>
 #include <functional>
@@ -340,12 +343,7 @@ inline std::string resolve_escape_sequence(const char *s, size_t n) {
 
 template <typename T> T token_to_number_(std::string_view sv) {
   T n = 0;
-#if __has_include(<charconv>)
-  if constexpr (!std::is_floating_point<T>::value) {
-    std::from_chars(sv.data(), sv.data() + sv.size(), n);
-#else
-  if constexpr (false) {
-#endif
+  if constexpr (CPPPEGLIB_HAS_CHARCONV && !std::is_floating_point<T>::value) {
     std::from_chars(sv.data(), sv.data() + sv.size(), n);
   } else {
     auto s = std::string(sv);