arg_heuristic(): be better prepared to handle path lists

If we were to handle only single paths, the buffer really would only
need to fit a single one, but arg_heuristic is also used to convert e.g.
INFO_PATH and MAN_PATH (which can contain multiple absolute POSIX-style
paths that need to be converted to Windows-style paths).

This is only really relevant if the POSIX root directory's path is
already pretty long. Such a beast has been spotted in the wild, in the
Git for Windows project:

	git-for-windows/git#303

Of course, this patch is only a work-around that helps in many, but not
all cases. Obviously this patch will wait patiently until a real fix
comes around the corner, and then readily retire.

Signed-off-by: Johannes Schindelin <[email protected]>

winsup/cygwin/path.cc

@@ -3451,7 +3451,9 @@ arg_heuristic_with_exclusions (char const * const arg, char const * exclusions,
       exclusions += strlen (exclusions) + 1;
     }
 
-  size_t stack_len = arglen + MAX_PATH;
+  // Leave enough room for at least 16 path elements; we might be converting
+  // a path list.
+  size_t stack_len = arglen + 16 * MAX_PATH;
   char * stack_path = (char *)malloc (stack_len);
   if (!stack_path)
     {