Adding conditional_t for pre-CPP14.

Author: RealTimeChris

include/fast_float/ascii_number.h

@@ -29,9 +29,9 @@ template <typename UC> fastfloat_really_inline constexpr bool has_simd_opt() {
 }
 
 template <typename value_type> struct get_equal_sized_uint {
-  using type = std::conditional_t<
+  using type = FASTFLOAT_CONDITIONAL_T(
       sizeof(value_type) == 4, uint32_t,
-      std::conditional_t<sizeof(value_type) == 2, uint16_t, uint8_t>>;
+      FASTFLOAT_CONDITIONAL_T(sizeof(value_type) == 2, uint16_t, uint8_t));
 };
 
 template <typename value_type>

include/fast_float/float_common.h

@@ -883,6 +883,40 @@ operator^=(chars_format &lhs, chars_format rhs) noexcept {
   return lhs = (lhs ^ rhs);
 }
 
+#if defined(_MSC_VER)
+#if _MSC_VER >= 1900
+#if _MSC_VER >= 1910
+#else
+#define CPP14_NOT_SUPPORTED
+#endif
+#else
+#define CPP14_NOT_SUPPORTED
+#endif
+#elif __cplusplus < 201402L
+#define CPP14_NOT_SUPPORTED
+#endif
+
+#ifndef CPP14_NOT_SUPPORTED
+#define FASTFLOAT_CONDITIONAL_T(condition, true_t, false_t)                    \
+  std::conditional_t<condition, true_t, false_t>
+#else
+template <bool condition, typename true_t, typename false_t>
+struct conditional {
+  using type = false_t;
+};
+
+template <typename true_t, typename false_t>
+struct conditional<true, true_t, false_t> {
+  using type = true_t;
+};
+
+template <bool condition, typename true_t, typename false_t>
+using conditional_t = typename conditional<condition, true_t, false_t>::type;
+
+#define FASTFLOAT_CONDITIONAL_T(condition, true_t, false_t)                    \
+  conditional_t<condition, true_t, false_t>
+#endif
+
 namespace detail {
 // adjust for deprecated feature macros
 constexpr chars_format adjust_for_feature_macros(chars_format fmt) {