Previous build of OpenSSH 7.5p1 broke due to undefined prototypes for
functions provided by LibreSSL, which then were called according to
the wrong calling convention.
We had this situation before in
https://github.com/OpenSMTPD/OpenSMTPD/issues/691
Build with -Werror now to detect new issues arising in the future.
Remove one obsolete constant value to make this pass.
Check OpenBSD libc functions (partially provided by glibc and musl)
using AC_CHECK_DECLS instead to verify they have a prototype.
Explicitly define prototypes for arc4random* when LibreSSL is detected
(from https://bugzilla.mindrot.org/show_bug.cgi?id=2465)
6118b964a5