Implement page table mirroring in apldart(4) and use that to enable the
IOMMU for the USB controllers on Apple Silicon.
Based on a diff from Heyang Zhou.
set CXX to prevent sccache detection via MODPY_PYBUILD=mesonpy; OK sthen
meson picks up /usr/local/bin/sccache if installed and prefers it to
"c++" in PATH, CXX from the environment takes precendence, but is not
set, causing PORTS_PRIVSEP=yes builds to fail.
(sccache supports Rust and C++, but bsd.port.mk(5) USE_SCCACHE=yes
only support C++ (so far), i.e. ${WRKDIR}/bin/c++ which CXX resolves
to is not effected by it.)
Fix free space check for unqualified filenames
In limited instances, fetch recieves an unqualified filename that
will be fetched into the current directory. The simple "dirname"
implementation wasn't smart enough.
