py3: use pycompat.sysargv in scmposix.systemrcpath()

sys.argv returns unicodes on Python 3. We have pycompat.sysargv which returns
bytes encoded using os.fsencode(). After this patch scmposix.systemrcpath()
returns bytes in Python 3 world. This change is also a part of making
`hg version` run in Python 3.

mercurial/scmposix.py

@@ -1,71 +1,72 b''
 from __future__ import absolute_import
 
 import array
 import errno
 import fcntl
 import os
 import sys
 
 from . import (
     encoding,
     osutil,
+    pycompat,
 )
 
 def _rcfiles(path):
     rcs = [os.path.join(path, 'hgrc')]
     rcdir = os.path.join(path, 'hgrc.d')
     try:
         rcs.extend([os.path.join(rcdir, f)
                     for f, kind in osutil.listdir(rcdir)
                     if f.endswith(".rc")])
     except OSError:
         pass
     return rcs
 
 def systemrcpath():
     path = []
     if sys.platform == 'plan9':
         root = 'lib/mercurial'
     else:
         root = 'etc/mercurial'
     # old mod_python does not set sys.argv
     if len(getattr(sys, 'argv', [])) > 0:
-        p = os.path.dirname(os.path.dirname(sys.argv[0]))
+        p = os.path.dirname(os.path.dirname(pycompat.sysargv[0]))
         if p != '/':
             path.extend(_rcfiles(os.path.join(p, root)))
     path.extend(_rcfiles('/' + root))
     return path
 
 def userrcpath():
     if sys.platform == 'plan9':
         return [encoding.environ['home'] + '/lib/hgrc']
     else:
         return [os.path.expanduser('~/.hgrc')]
 
 def termsize(ui):
     try:
         import termios
         TIOCGWINSZ = termios.TIOCGWINSZ  # unavailable on IRIX (issue3449)
     except (AttributeError, ImportError):
         return 80, 24
 
     for dev in (ui.ferr, ui.fout, ui.fin):
         try:
             try:
                 fd = dev.fileno()
             except AttributeError:
                 continue
             if not os.isatty(fd):
                 continue
             arri = fcntl.ioctl(fd, TIOCGWINSZ, '\0' * 8)
             height, width = array.array('h', arri)[:2]
             if width > 0 and height > 0:
                 return width, height
         except ValueError:
             pass
         except IOError as e:
             if e[0] == errno.EINVAL:
                 pass
             else:
                 raise
     return 80, 24