don't define constants unused in release build (SGI CC warning)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@35630 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/datetime.cpp

@@ -235,11 +235,14 @@ static const long MILLISECONDS_PER_DAY = 86400000l;
 // (i.e. JDN(Jan 1, 1970) = 2440587.5)
 static const long EPOCH_JDN = 2440587l;
 
+// used only in asserts
+#ifdef __WXDEBUG__
 // the date of JDN -0.5 (as we don't work with fractional parts, this is the
 // reference date for us) is Nov 24, 4714BC
 static const int JDN_0_YEAR = -4713;
 static const int JDN_0_MONTH = wxDateTime::Nov;
 static const int JDN_0_DAY = 24;
+#endif // __WXDEBUG__
 
 // the constants used for JDN calculations
 static const long JDN_OFFSET         = 32046l;