Mk/Uses/python.mk's PEP517_BUILD_CMD now places wheel output in ${WRKDIR}/whl
rather than the build backend's default dist directory, which varies by
backend (e.g. ${WRKSRC}/dist for build/setuptools). Ports that override
PEP517_BUILD_CMD or PEP517_INSTALL_CMD directly, or invoke a build tool on
their own (e.g. maturin), bypassing the new default, must follow suit: build
commands (python -m build, python -m flit_core.wheel, maturin build, ...) now
pass ${WRKDIR}/whl as their dist directory (--outdir, -o, ...) instead of
their previous, backend-specific default, and install commands that glob for
the built wheel look there too.