Don't use _ecvt (#233)

format.h

@@ -228,7 +228,6 @@ typedef std::numeric_limits<fmt::internal::DummyInt> FPUtil;
 // if the latter are not available.
 inline DummyInt signbit(...) { return DummyInt(); }
 inline DummyInt _ecvt_s(...) { return DummyInt(); }
-inline DummyInt _ecvt(...) { return DummyInt(); }
 inline DummyInt isinf(...) { return DummyInt(); }
 inline DummyInt _finite(...) { return DummyInt(); }
 inline DummyInt isnan(...) { return DummyInt(); }
@@ -273,12 +272,8 @@ class numeric_limits<fmt::internal::DummyInt> :
     if (x < 0) return true;
     if (!isnotanumber(x)) return false;
     int dec = 0, sign = 0;
-    if (sizeof(_ecvt_s(0, 0, x, 0, 0, 0)) == sizeof(int)) {
-      char buffer[2];  // The buffer size must be >= 2 or _ecvt_s will fail.
-      _ecvt_s(buffer, sizeof(buffer), x, 0, &dec, &sign);
-      return sign != 0;
-    }
-    _ecvt(x, 0, &dec, &sign);
+    char buffer[2];  // The buffer size must be >= 2 or _ecvt_s will fail.
+    _ecvt_s(buffer, sizeof(buffer), x, 0, &dec, &sign);
     return sign != 0;
   }
 };