Fix usage of date library

For backwards compatibility reasons, the date library does not use the
new C++17 uncaught_exception signature, even if compiling under C++17.

With GCC 10, libstdc++ marks the old uncaught_exception signature as
deprecated, so this causes a compilation error.

Fortunately, date library provides a way to select which
uncaught_exception version to use, so force using the new version.

Signed-off-by: sephiroth99 <sephiroth99@gmail.com>

src/xenia/kernel/xclock.h

@@ -14,6 +14,8 @@
 
 #include "xenia/base/clock.h"
 
+// https://github.com/HowardHinnant/date/commit/5ba1c1ad8514362dba596f228eb20eb13f63d948#r33275526
+#define HAS_UNCAUGHT_EXCEPTIONS 1
 #include "third_party/date/include/date/date.h"
 
 namespace xe {