bug#31891: emacs-realgud fails to build

[Maxim Cournoyer]

Our emacs-realgud package is now failing, maybe since we've moved to
Emacs 26.1.

The error reads like:

--8<---------------cut here---------------start------------->8---
configure: "Checking prerequiste packages"
Trailing garbage following expression: 
   )
configure: error: Can't continue until above error is corrected.
Backtrace:
           4 (primitive-load "/gnu/store/sllkla5k0jaxr8zqvzirif6ysay…")
In ice-9/eval.scm:
   191:35  3 (_ _)
In srfi/srfi-1.scm:
    640:9  2 (for-each #<procedure a3f0c0 at /gnu/store/alkhgfm87dh…> …)
In 
/gnu/store/alkhgfm87dh8r5bdi81dls8wyjlc1yxp-module-import/guix/build/gnu-build-system.scm:
   799:31  1 (_ _)
In 
/gnu/store/alkhgfm87dh8r5bdi81dls8wyjlc1yxp-module-import/guix/build/utils.scm:
    616:6  0 (invoke _ . _)

/gnu/store/alkhgfm87dh8r5bdi81dls8wyjlc1yxp-module-import/guix/build/utils.scm:616:6:
 In procedure invoke:
Throw to key `srfi-34' with args `(#<condition &invoke-error [program: "sh" 
arguments: ("autogen.sh") exit-status: 1 term-signal: #f stop-signal: #f] 
987f80>)'.
builder for 
`/gnu/store/4spv2r6b5yddz5ffs8kmkn548crfrbdq-emacs-realgud-1.4.5.drv' failed 
with exit code 1
guix package: error: build failed: build of
`/gnu/store/4spv2r6b5yddz5ffs8kmkn548crfrbdq-emacs-realgud-1.4.5.drv' failed
--8<---------------cut here---------------end--------------->8---

I'll try fixing it, but I have other bugs to close before, so feel free
to beat me to it!

Maxim