Add meson awareness to numpy helper and python3-pep517 style

[ahesford]

Now that a meson build helper exists, we can further remove redundancy in some numeric python packages. In addition to the two cleaned up here, I believe we have some pending PRs that would benefit from these changes.

While I'm touching the numpy helper, I might as well fix its missing documentation.

cc: @tornaria

Testing the changes

• I tested the changes in this PR: YES

[tornaria]

LGTM, do you want to cleanup make_build_args in pylint?

A (very) minor nitpick: maybe [[ "${build_helper}" = *meson* ]] should be [[ " ${build_helper} " = *" meson "* ]], etc.

But the idiom is used all over the place and currently there is no conflict possible.

[ahesford]

A (very) minor nitpick: maybe [[ "${build_helper}" = *meson* ]] should be [[ " ${build_helper} " = *" meson "* ]], etc.

Adding spaces might thwart a match when the variable embeds a newline, like

build_helper="
 meson
 numpy
"

which probably never ought to happen, but could cause hard-to-discover issues when it does. What we really need is to turn these space-separated variables into proper arrays so that we can test for membership the right way.

Thanks for reminding me about pylint; I'll add a fix here.

[tornaria]

You may want to cherry-pick 0a2141b from #46109, to further cleanup the scipy template (no need for the pybind11 thing).

I wonder about this:

	if [ "$CROSS_BUILD" ]; then
		# Meson can't tolerate $CC with arguments as set by the build helper
		CC="${XBPS_CROSS_TRIPLET}-gcc"
		# CXX needs to know where to find Python headers
		CXXFLAGS+=" -I${XBPS_CROSS_BASE}/${py3_inc}"
	fi

Is this necessary? I didn't add this to python3-contourpy and I had no trouble... This block is there both in scipy and scikit-image.

[tornaria]

Aha, it probably refers to the python3 build helper, which is no longer used...

[ahesford]

The python3 build helper is automatically pulled in by the python3 build styles. I haven't tested whether it can be removed now, but it was definitely needed when it was added.

[ahesford]

Closed in 0fcff10 with some additional changes:

• pylint cleanup
• Adopt python3-pybind11 "system" installation, slightly differently than in python3-matplotlib: update to 3.8.0, also update deps #46109
• Massive cleanup of python3-{scipy,scikit-image}, including removal of obsolete $CC and $CXXFLAGS overrides.