fix MKL tests in Github Actions

The most recent version of MKL on PyPI ships only `libmkl_rt.so.1`, not
`libmkl_rt.so`. In Nutils we load the latter. This causes two problems: in
Github Actions we cannot find the location of the library directory where MKL
is being installed, because we explicitly look for `libmkl_rt.so` and Nutils
can't load the library because we explicitly load the missing unversioned
library. This patch fixes both problems by searching for the versioned library
and adding a symlink to the unversioned library.

.github/workflows/test.yaml

@@ -100,13 +100,12 @@ jobs:
           # Install Nutils from `dist` dir created in job
           # `build-python-package`.
           python -um pip install --no-index --find-links ./dist nutils
-      - name: Get library directory
-        id: get-lib-dir
+      - name: Configure MKL
+        id: configure-mkl
         if: ${{ matrix.matrix-backend == 'mkl' }}
-        run: python -um devtools.gha.get_lib_dir
+        run: python -um devtools.gha.configure_mkl
       - name: Test
         env:
-          LD_LIBRARY_PATH: ${{ steps.get-lib-dir.outputs.libdir }}
           NUTILS_DEBUG: all
         run: |
           mkdir testenv

devtools/gha/configure_mkl.py

@@ -0,0 +1,25 @@
+from .. import log
+import sys, site, os
+
+libsubdir = 'lib'
+prefixes = list(site.PREFIXES)
+if hasattr(site, 'getuserbase'):
+  prefixes.append(site.getuserbase())
+for prefix in prefixes:
+  libdir = os.path.join(prefix, libsubdir)
+  if not os.path.exists(os.path.join(libdir, 'libmkl_rt.so.1')):
+    continue
+  log.set_output('libdir', libdir)
+  break
+else:
+  log.error('cannot find {} in any of the following dirs: {}'.format('libmkl_rt.so.1', ' '.join(prefixes)))
+
+lib = os.path.join(libdir, 'libmkl_rt.so')
+if not os.path.exists(lib):
+  os.symlink('libmkl_rt.so.1', lib)
+
+github_env = os.environ.get('GITHUB_ENV')
+assert github_env
+ld_library_path = ':'.join(filter(None, (os.environ.get('LD_LIBRARY_PATH', ''), libdir)))
+with open(github_env, 'a') as f:
+  print('LD_LIBRARY_PATH={}'.format(ld_library_path), file=f)