aclocal.m4: add minimal support for nios2 architecture

Authored by trofi on Dec 25 2017, 9:46 AM.

Description

aclocal.m4: add minimal support for nios2 architecture

With this change unregisterised port can already produce minimal
executables:

ELF 32-bit LSB executable, Altera Nios II, version 1 (SYSV),
dynamically linked, interpreter /lib/ld-linux-nios2.so.1

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>