build: check-final-inputs-self-contained has an exception for 'bash:include'.

Currently 'bash:include' of the final Bash depends on bootstrap stuff.

* build-aux/check-final-inputs-self-contained.scm (final-inputs): Add
clause for 'bash:include'.
* gnu/packages/commencement.scm (bash-final): Add FIXME comment.

gnu/packages/commencement.scm

@@ -783,6 +783,7 @@ exec ~a/bin/~a-~a -B~a/lib -Wl,-dynamic-linker -Wl,~a/~a \"$@\"~%"
 (define bash-final
   ;; Link with `-static-libgcc' to make sure we don't retain a reference
   ;; to the bootstrap GCC.
+  ;; FIXME: This depends on 'bootstrap-binaries' via Makefile.in.
   (package-with-bootstrap-guile
    (package-with-explicit-inputs (static-libgcc-package bash)
                                  %boot3-inputs