Smooth out cross-compiling for aarch64
This MR contains some build configuration updates and fixes that address a few issues I ran into when cross-compiling Parabix.
Specifically, this MR:
- Adds an option for setting the object cache directory statically or determining it at runtime. This is useful when cc'ing as the path on the target will be different if using
$HOME/.parabix
. - Adds a check for the
aarch64
target alongsidearm64
- Fixes an issue where the
FindZ3.cmake
script was failing to parse the version header