[clang-format][PR46043] Parse git config w/ implicit values

[JakeMerdichAMD]

Summary

https://bugs.llvm.org/show_bug.cgi?id=46043

Git's config is generally of the format 'key=val', but a setting
'key=true' can be written as just 'key'. The git-clang-format script
expects a value and crashes in this case; this change handles implicit
'true' values in the script.

[MyDeveloperDay]

LGTM

clang/tools/clang-format/git-clang-format

def load_git_config(non_string_options=None):
   All options are assumed to be strings unless in `non_string_options`, in which
   is a dictionary mapping option name (in lower case) to either "--bool" or
   "--int"."""
   if non_string_options is None:
     non_string_options = {}
   out = {}
   for entry in run('git', 'config', '--list', '--null').split('\0'):
     if entry:
+      if '\n' in entry:
         name, value = entry.split('\n', 1)
+      else:
+        # A setting with no '=' ('\n' with --null) is implicitly 'true'
+        name = entry
+        value = 'true'
       if name in non_string_options:
         value = run('git', 'config', non_string_options[name], name)
       out[name] = value
   return out
 
 
 def interpret_args(args, dash_dash, default_commit):
   """Interpret `args` as "[commits] [--] [files]" and return (commits, files).