Trac #32746: fedora-{26,27,...,34}-minimal: scipy build fails - openblas not found

for example, `fedora-34-minimal`
https://github.com/mkoeppe/sage/runs/3968544625?check_suite_focus=true

{{{
Note: CFLAGS, CXXFLAGS and SHAREDFLAGS are taken from distutils,
      so their current settings are ignored.
Installing scipy-1.6.3
Processing /sage/local/var/lib/sage/venv-
python3.9.7/var/tmp/sage/build/scipy-1.6.3/src
    Preparing wheel metadata: started
    Running command /sage/local/var/lib/sage/venv-
python3.9.7/bin/python3 /sage/local/var/lib/sage/venv-
python3.9.7/lib/python3.9/site-
packages/pip/_vendor/pep517/in_process/_in_process.py
prepare_metadata_for_build_wheel /tmp/tmpatw3swb6
    setup.py:462: UserWarning: Unrecognized setuptools command
('dist_info --egg-base /tmp/pip-modern-metadata-assu7gnc'), proceeding
with generating Cython sources and expanding templates
      warnings.warn("Unrecognized setuptools command ('{}'), proceeding
with "
    Running from SciPy source directory.
    lapack_opt_info:
[...]
    lapack_info:
      libraries openblas not found in ['/sage/local/var/lib/sage/venv-
python3.9.7/lib', '/usr/local/lib64', '/usr/local/lib', '/usr/lib64',
'/usr/lib', '/usr/lib/']
      NOT AVAILABLE

    /sage/local/var/lib/sage/venv-python3.9.7/lib/python3.9/site-
packages/numpy/distutils/system_info.py:1858: UserWarning:
        Lapack (http://www.netlib.org/lapack/) libraries not found.
        Directories to search for the libraries can be specified in the
        numpy/distutils/site.cfg file (section [lapack]) or by setting
        the LAPACK environment variable.
      return getattr(self, '_calc_info_{}'.format(name))()
    lapack_src_info:
      NOT AVAILABLE

    /sage/local/var/lib/sage/venv-python3.9.7/lib/python3.9/site-
packages/numpy/distutils/system_info.py:1858: UserWarning:
        Lapack (http://www.netlib.org/lapack/) sources not found.
        Directories to search for the sources can be specified in the
        numpy/distutils/site.cfg file (section [lapack_src]) or by
setting
        the LAPACK_SRC environment variable.
      return getattr(self, '_calc_info_{}'.format(name))()
      NOT AVAILABLE

    Traceback (most recent call last):
      File "/sage/local/var/lib/sage/venv-python3.9.7/lib/python3.9
/site-packages/pip/_vendor/pep517/in_process/_in_process.py", line 349,
in <module>
        main()
      File "/sage/local/var/lib/sage/venv-python3.9.7/lib/python3.9
/site-packages/pip/_vendor/pep517/in_process/_in_process.py", line 331,
in main
        json_out['return_val'] = hook(**hook_input['kwargs'])
      File "/sage/local/var/lib/sage/venv-python3.9.7/lib/python3.9
/site-packages/pip/_vendor/pep517/in_process/_in_process.py", line 151,
in prepare_metadata_for_build_wheel
        return hook(metadata_directory, config_settings)
      File "/sage/local/var/lib/sage/venv-python3.9.7/lib/python3.9
/site-packages/setuptools/build_meta.py", line 166, in
prepare_metadata_for_build_wheel
        self.run_setup()
      File "/sage/local/var/lib/sage/venv-python3.9.7/lib/python3.9
/site-packages/setuptools/build_meta.py", line 258, in run_setup
        super(_BuildMetaLegacyBackend,
      File "/sage/local/var/lib/sage/venv-python3.9.7/lib/python3.9
/site-packages/setuptools/build_meta.py", line 150, in run_setup
        exec(compile(code, __file__, 'exec'), locals())
      File "setup.py", line 598, in <module>
        setup_package()
      File "setup.py", line 594, in setup_package
        setup(**metadata)
      File "/sage/local/var/lib/sage/venv-python3.9.7/lib/python3.9
/site-packages/numpy/distutils/core.py", line 135, in setup
        config = configuration()
      File "setup.py", line 500, in configuration
        raise NotFoundError(msg)
    numpy.distutils.system_info.NotFoundError: No BLAS/LAPACK libraries
found.
    To build Scipy from sources, BLAS & LAPACK libraries need to be
installed.
    See site.cfg.example in the Scipy source directory and
    https://docs.scipy.org/doc/scipy/reference/building/index.html for
details.
    Preparing wheel metadata: finished with status 'error'
}}}

This is another regression caused by #32442 (`./configure`: Make
`--with-sage-venv=auto` the default).

URL: https://trac.sagemath.org/32746
Reported by: mkoeppe
Ticket author(s): Matthias Koeppe
Reviewer(s): John Palmieri

Author: Release Manager

build/pkgs/numpy/spkg-install.in

@@ -16,7 +16,11 @@ if [ "$UNAME" = "CYGWIN" ]; then
     export CPPFLAGS="${CPPFLAGS} -D_GNU_SOURCE"
 fi
 
-python3 ../lapack_conf.py
+# Trac #32746: pkg-config omits -I and -L flags that refer to directories
+# that are already on CPATH, LIBRARY_PATH.
+# But our script tries to obtain the list of include_dirs and library_dirs
+# from pkg-config!
+(unset CPATH LIBRARY_PATH; python3 ../lapack_conf.py)
 
 # Make sure that the fortran objects are compiled with -fPIC
 export FFLAGS="$FFLAGS -fPIC"