Ah, my bad... my brain was so focused on 'custom' that it read 'custombuild' and thought you also had a custom makefile.
Strange that there is no -std=gnu99 in the downloaded Makefile.
A custom Makefile can be placed in /usr/local/directadmin/custombuild/custom/exim/Makefile, see Support for a...
That was the issue, I forgot that a custom Makefile was in use to support SRS.
And of course I had to read the release notes... (Exim 4.93 has been released)
Adding USE_OPENSSL=yes and adding -std=gnu99 to CFLAGS did the trick.
Thanks for the suggestions.
@Zhenyapan ./build update already downloads it fresh.
But without this step and immediately doing a ./build exim after changing the download server results in the same, except the first lines being:
Downloading exim-4.93.0.4.tar.gz...
--2020-01-16 12:15:52--...
Unfortunately we have the same issue here.
rm -rf exim-4.93.0.4
rm -f exim-4.93.0.4.tar.gz
edit options.conf and set downloadserver=filesX.directadmin.comm with 'X' being 1 to 7
./build update && ./build exim
Every time results in:
Found /usr/local/directadmin/custombuild/exim-4.93.0.4.tar.gz...