replace calls to 'uname -p' by 'uname -m'

Using 'uname -p' is broken on some distros (does not work in
Gentoo, Arch, maybe others). The recommended way to fetch the
arch is by using 'uname -m'.
limit the number of concurrent jobs to 8

Having too many concurrent jobs might hang the build process, it's
safer to limit the ammount to 8. The magic number 8 comes from the
build process for the OpenJDK PowerPC/AIX Port (JEP 175).
add build support for ppc64
update OBF_BASE_ARCH to include ppc64 arch