Try to fix building on kFreeBSD Upstream's build system fails to detect GNU/kFreeBSD because its uname output is unique. This patch sets its uname to match the regular FreeBSD build parameters. It also sets the target build directory to always be "installdir" (rather than uname-arch). We only build for one architecture at a time, anyway, and this way, we don't have to figure out which system we're building on and mangle the uname string depending on whether we're Linux or kFreeBSD.
Adjust paths for helper scripts to be found ATAC uses some generically named scripts (like "makeplots") that can't sensibly be placed in /usr/bin. We put them instead in /usr/lib/atac and adjust the driver script to be able to find them there.
Replace distutils.sysconfig with the stdlib sysconfig sysconfig has been available since Python 3.2 https://docs.python.org/3/library/sysconfig.html#module-sysconfig
