Add patch to disable sandbox ptracing

The Portage sandbox wants to invoke ptrace during the glibc
installation.  The ptrace syscall is not supported under qemu-user.
Disabling the Portage sandbox doesn't help.  Patch the sandbox to remove
ptrace support.

See: https://bugs.gentoo.org/648516

Containerfile

@@ -18,6 +18,7 @@ COPY --from=nest-overlay / /var/db/repos/nest/
 # Update, then rebuild all packages using a custom profile
 RUN eselect profile set "nest:${PROFILE}"
 RUN emerge --info
+RUN emerge -v --oneshot sys-apps/sandbox
 RUN emerge -v --update --deep --newuse --with-bdeps=y @world
 RUN emerge --depclean
 RUN emerge -v --emptytree @world

portage/patches/sys-apps/sandbox/sandbox-disable-ptrace-for-qemu-user.patch

+diff -ur sandbox-2.20.orig/configure sandbox-2.20/configure
+--- sandbox-2.20.orig/configure	2021-01-05 12:01:39.035638914 -0500
++++ sandbox-2.20/configure	2021-01-05 12:02:08.995021286 -0500
+@@ -2535,7 +2535,6 @@
+ as_fn_append ac_func_list " openat64"
+ as_fn_append ac_func_list " pathconf"
+ as_fn_append ac_func_list " process_vm_readv"
+-as_fn_append ac_func_list " ptrace"
+ as_fn_append ac_func_list " realpath"
+ as_fn_append ac_func_list " remove"
+ as_fn_append ac_func_list " renameat"