[jhbuild/BUG_lib64] defaults.jhbuildrc: fix detection of /usr/lib64 on Fedora

[Nelson Ben <nbenitez src gnome org>]

commit 71b380c51256bdc2997de5e572311221ae0ba902
Author: Nelson Benítez León <nbenitezl gmail com>
Date:   Tue Jun 30 13:24:19 2020 -0400

    defaults.jhbuildrc: fix detection of /usr/lib64 on Fedora
    
    Fixes #67, see issue for details.
    
    Thanks Peter Simonyi for issue debugging and fix proposal.

 jhbuild/defaults.jhbuildrc | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)
---
diff --git a/jhbuild/defaults.jhbuildrc b/jhbuild/defaults.jhbuildrc
index eb3dbe42..dc99e7e9 100644
--- a/jhbuild/defaults.jhbuildrc
+++ b/jhbuild/defaults.jhbuildrc
@@ -145,11 +145,11 @@ export_dir = None
 
 # attempt to detect the system library path
 extra_prefixes = []
-try:
+if hasattr(sys.implementation, '_multiarch') and \
+   os.path.exists('/usr/lib/' + sys.implementation._multiarch):
     # Debian-style multiarch
     system_libdirs = ['/usr/lib/' + sys.implementation._multiarch, '/usr/lib']
-
-except AttributeError:
+else:
     # Check the python path and make some reasonable guesses
     system_libdirs = []
     for path in sys.path: