elfloader-*: Add exit / shutdown configuration

Add graceful shutdown configuration to `Config.uk` files for elfloader
apps. With this, binary-compatible apps that end their execution will
also result in ending the VMM process (QEMU or Firecracker).

Signed-off-by: Razvan Deaconescu <[email protected]>

Author: razvand

elfloader-basic/Config.uk

@@ -30,3 +30,8 @@ default y
 	select LIBUKCPIO
 	select LIBDEVFS
 	select LIBDEVFS_AUTOMOUNT
+
+	# Add multithreading support to run exit() calls.
+	select LIBUKBOOT_MAINTHREAD
+	select LIBUKBOOT_SHUTDOWNREQ_HANDLER
+	select LIBPOSIX_PROCESS_MULTITHREADING

elfloader-net/Config.uk

@@ -31,6 +31,11 @@ default y
 	select LIBDEVFS
 	select LIBDEVFS_AUTOMOUNT
 
+	# Add multithreading support to run exit() calls.
+	select LIBUKBOOT_MAINTHREAD
+	select LIBUKBOOT_SHUTDOWNREQ_HANDLER
+	select LIBPOSIX_PROCESS_MULTITHREADING
+
 	# Select LWIP networking stack library.
 	select LIBLWIP