Fix FileNotFoundError when restorecon unavailable

Fixes:
 - http://autobuild.buildroot.net/results/d5dcdfdfab3503fdc387f99e68267972a38c417d

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>

mesonbuild/scripts/meson_install.py

@@ -97,6 +97,10 @@ def restore_selinux_contexts():
         # is ignored quietly.
         return
 
+    if not shutil.which('restorecon'):
+        # If we don't have restorecon, failure is ignored quietly.
+        return
+
     with subprocess.Popen(['restorecon', '-F', '-f-', '-0'],
                           stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE) as proc:
         out, err = proc.communicate(input=b'\0'.join(os.fsencode(f) for f in selinux_updates) + b'\0')