I have recently upgraded from unRAID v5 to v6. I was able to compile Mediainfo from source on v5. I had the gcc and g++ compilers installed. I have installed gcc and g++ and make 64bit packages from here: http://mirrors.slackware.com/slackware/slackware64-14.1/slackware64/d/
When I run the compile script "CLI_Compile.sh" I get the following:
checking build system type... x86_64-unknown-linux-gnu
checking for a BSD-compatible install... /usr/bin/ginstall -c
checking whether build e
I figured it out by looking at the "config.log". Every time it had an error, I would need to download a package with a library or function which got me a little further each time. In V5 the gcc package through unMenu installed: gcc, make, binutils, glibc, and kernel-headers. That was the difference between V5 and V6 ( I am not running unMENU on V6 yet).
I ended up with these packages in my /boot/extra folder:
binutils-2.23.52.0.1-x86_64-2.txz
gcc-4.8.2-x86_64-1.txz
gcc-g++-4.8.2-x8