Hard code year::min(), year::max() to [-32767, 32767]

* When year < 0, -year > 0 (always).
* These are the minimal limits C places on short.
* Reserving -32768 is useful in the implementation.

date.h

@@ -1455,7 +1455,7 @@ inline
 year
 year::min() NOEXCEPT
 {
-    return year{std::numeric_limits<short>::min()+1};
+    return year{-32767};
 }
 
 CONSTCD11
@@ -1463,7 +1463,7 @@ inline
 year
 year::max() NOEXCEPT
 {
-    return year{std::numeric_limits<short>::max()};
+    return year{32767};
 }
 
 CONSTCD11