bootstrap: Compile with 64-bit time_t on 32-bit Linux if possible

Extend commit 1b9e8f833f (Linux: Compile with 64-bit time_t even on
32-bit architectures, 2025-06-26, v4.1.0-rc2~16^2) to `bootstrap`.

bootstrap

@@ -1848,7 +1848,7 @@ fi
 system_flags=''
 case "${cmake_system}" in
   # Ensure filesystem access uses 64-bit offsets even on 32-bit hosts.
-  *Linux*) system_flags='-D_FILE_OFFSET_BITS=64' ;;
+  *Linux*) system_flags='-D_FILE_OFFSET_BITS=64 -D_TIME_BITS=64' ;;
 esac
 if test "x${system_flags}" != "x"; then
   cmake_c_flags="${cmake_c_flags} ${system_flags}"