bad file descriptor / bad substitution

Please find attached here a tarball:

that contains a minimal configure.ac, the configure script
resulting from running ‘autoreconf -vfi’, and a log of both the
autoreconf run and the subsequent ./configure invocation.
(Altogether four files.)

The file configure.out shows the error:


Question: Is this a simple case of user error (‘AC_CHECK_DECLS’
should be m4-quoted), or is this a legitimate Autoconf bug?

If there is anything else i can provide to resolve this issue,
please let me know.

-- 
Thien-Thi Nguyen -----------------------------------------------
 (defun responsep (query)               ; (2021) Software Libero
   (pcase (context query)               ;       = Dissenso Etico
     (`(technical ,ml) (correctp ml))
     ...))                              748E A0E8 1CB8 A748 9BFA
--------------------------------------- 6CE4 6703 2224 4C80 7502

./configure: line 1486: 5: Bad file descriptor
checking whether  is declared... ./configure: line 1488: ${+y}: bad substitution

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