The autoconf script for libassuan were fixed in this commit: https://dev.gnupg.org/rAb9b7f1cf3fd0228fd31cb62a144628ee8ad26953

However, this fix wasn't propagated to other projects that carry the assuan m4 (usually in m4/libassuan.m4), resulting in issues when building with libassuan 3.x like:

In file included from sysutils.c:32:0:
../config.h:650:33: error: token "$" is not valid in preprocessor expressions
 #define LIBASSUAN_API_REQUESTED $req_libassuan_api
                                 ^

The AC_DEFINE_UNQUOTED fix should be added to those projects (and any others I didn't mention).