distutils-r1.eclass: fix multiple impl handling for setuptools package

In the latest version of setuptools, setuptools stopped explicitly
excluding the build/ directory:
pypa/setuptools#4211

It is the default build_base until we specially set it via
$DIST_EXTRA_CONFIG -- and before then, by rm -rf'ing the build/
directory.

Both approaches were guarded by checking if DISTUTILS_USE_PEP517 is set
to setuptools. This doesn't work for the setuptools package itself,
since setuptools builds "standalone" so that it can depend on its own
in-tree backend.

Result: setuptools has always been ignoring BUILD_DIR and leaving
persistent files around. Somehow that led to the new version of
setuptools without `options.packages.find -> exclude = build`,
installing a bunch of new files when building for multiple PYTHON_COMPAT
targets. From iwdevtools:

 *  FILES:+usr/lib/python3.12/site-packages/build/lib/setuptools/wheel.py

[...]

 *   SIZE: 13.88MiB -> 20.44MiB, 1083 -> 1631 files
 * ------> FILES(+556,-8) SIZE(+47.22%)

(It should be noted that as part of the upgrade itself, python3_11 did
get +12,-4 files, which is vastly out of proportion to the combined
total of 556. This should actually be +24,-8.)

Fix by running setuptools based code for standalone build-backends (and
pbr, a setuptools wrapper) as well. It is either unneeded or necessary,
but shouldn't hurt.

Signed-off-by: Eli Schwartz <[email protected]>

Author: eli-schwartz

eclass/distutils-r1.eclass

@@ -1506,7 +1506,10 @@ distutils-r1_python_compile() {
 	_python_check_EPYTHON
 
 	case ${DISTUTILS_USE_PEP517:-setuptools} in
-		setuptools)
+		# pbr is a setuptools wrapper. Standalone may or may not
+		# wrap setuptools (the setuptools package itself does!)
+		# so better to do too much rather than too little.
+		setuptools|pbr|standalone)
 			# call setup.py build when using setuptools (either via PEP517
 			# or in legacy mode)