Re: autogen.sh and configure errors

[Eli Zaretskii]

> From: Arthur Miller <arthur.miller@live.com>
> Date: Sat, 02 Jan 2021 15:12:24 +0100
> 
> configure.ac:1771: warning: Checking for headers with the preprocessor is
> configure.ac:1771: deprecated. Specify prerequisite code to AC_CHECK_HEADER
> configure.ac:1771: instead of using fourth argument `-'. (Many headers need
> configure.ac:1771: no prerequisites. If you truly need to test whether
> configure.ac:1771: something passes the preprocessor but not the compiler,
> configure.ac:1771: use AC_PREPROC_IFELSE.)
> ./lib/autoconf/headers.m4:115: _AC_CHECK_HEADER_PREPROC is expanded from...
> ./lib/autoconf/headers.m4:56: AC_CHECK_HEADER is expanded from...
> ./lib/autoconf/headers.m4:217: AC_CHECK_HEADERS is expanded from...

I don't have a 'lib/autoconf' subdirectory, nor the file headers.m4
anywhere in the Emacs tree.  Where did they come from?