Handle two corner cases in creduce-clang-crash.py

[rnk]

Summary

First, call os.path.normpath on the filename argument. I passed in
./foo-asdf.cpp, and this meant that the script failed to find the
filename, and bad things happened.

Second, call os.path.abspath on binaries. CReduce runs the
interestingness test in a temp dir, so relative paths will not work.

[akhuang]

lgtm

clang/utils/creduce-clang-crash.py

 clang_cmd = None
 not_cmd = None
 
 def verbose_print(*args, **kwargs):
   if verbose:
     print(*args, **kwargs)
 
 def check_file(fname):
+  fname = os.path.normpath(fname)
   if not os.path.isfile(fname):
     sys.exit("ERROR: %s does not exist" % (fname))
   return fname
 
 def check_cmd(cmd_name, cmd_dir, cmd_path=None):
   """
   Returns absolute path to cmd_path if it is given,
   or absolute path to cmd_dir/cmd_name.
   """
   if cmd_path:
+    # Make the path absolute so the creduce test can be run from any directory.
+    cmd_path = os.path.abspath(cmd_path)
     cmd = find_executable(cmd_path)
     if cmd:
       return cmd
     sys.exit("ERROR: executable `%s` not found" % (cmd_path))
 
   cmd = find_executable(cmd_name, path=cmd_dir)
   if cmd:
     return cmd