third_party/sandboxroot: add libstdc++-static

Change-Id: I5528cfe7a218be10448d7b000756ddcd196cdd4d
Reviewed-on: https://review.monogon.dev/c/monogon/+/1441
Reviewed-by: Serge Bazanski <serge@monogon.tech>
Tested-by: Jenkins CI
diff --git a/third_party/sandboxroot/regenerate.sh b/third_party/sandboxroot/regenerate.sh
index 698098f..76b9a90 100755
--- a/third_party/sandboxroot/regenerate.sh
+++ b/third_party/sandboxroot/regenerate.sh
@@ -13,6 +13,10 @@
   "python-unversioned-command"
   "glibc-static"
 
+  # Required to build static CGO binaries
+  # see monogon-dev/monogon#192
+  "libstdc++-static"
+
   # Kernel build
   "flex"
   "bison"