guix: Enable CET for glibc package

contrib/guix/manifest.scm

@@ -469,6 +469,7 @@ inspecting signatures in Mach-O binaries.")
           `(append ,flags
             ;; https://www.gnu.org/software/libc/manual/html_node/Configuring-and-compiling.html
             (list "--enable-stack-protector=all",
+                  "--enable-cet",
                   "--enable-bind-now",
                   "--disable-werror",
                   building-on)))