commit 9735dcb16c00bc7087e9a88c46bad6ed65df3922
Author: Sam Thursfield <sam@afuera.me.uk>
Date:   Fri Apr 14 13:02:35 2017 +0100

    Fix 'Bad file descriptor' error when checking libtool version
    
    Running g-ir-scanner on Fedora 25 (libtool 2.4.6) produces the following
    message on stderr, twice:
    
        /usr/bin/libtool: line 2460: printf: write error: Bad file descriptor
    
    This is because we were redirecting stdout to /dev/null incorrectly --
    we were opening /dev/null for reading rather than for writing.

diff --git a/giscanner/utils.py b/giscanner/utils.py
index aff5393..da848d5 100644
--- a/giscanner/utils.py
+++ b/giscanner/utils.py
@@ -159,7 +159,7 @@ def get_libtool_command(options):
         libtool_cmd = 'glibtool'
     try:
         subprocess.check_call([libtool_cmd, '--version'],
-                              stdout=open(os.devnull))
+                              stdout=open('/dev/null', 'w'))
     except (subprocess.CalledProcessError, OSError):
         # If libtool's not installed, assume we don't need it
         return None
