libarchive: Update to build within CMake

Hard-code more libarchive options as internal cache entries.  Doing so
makes some of our `IF(0)` conditions unnecessary, so remove those.

Source/cm_get_date.c

@@ -2,6 +2,10 @@
    file Copyright.txt or https://cmake.org/licensing for details.  */
 #include "cm_get_date.h"
 
+// FIXME: This suppresses use of localtime_r because archive_getdate.c
+// depends the rest of libarchive's checks for that.
+#define CM_GET_DATE
+
 #define __archive_get_date cm_get_date
 
 #include "../Utilities/cmlibarchive/libarchive/archive_getdate.c"