DOS/Windows-specific code: exec.c and symfile.c

[Eli Zaretskii <eliz at is dot elta dot co dot il>]

    * exec.c:exec_file_attach()

	  scratch_chan = openp (getenv ("PATH"), 1, filename,
		       write_files ? O_RDWR | O_BINARY : O_RDONLY | O_BINARY, 0,
				&scratch_pathname);
    #if defined(__GO32__) || defined(_WIN32) || defined(__CYGWIN__)
	  if (scratch_chan < 0)
	    {
	      char *exename = alloca (strlen (filename) + 5);
	      strcat (strcpy (exename, filename), ".exe");
	      scratch_chan = openp (getenv ("PATH"), 1, exename, write_files ?
		 O_RDWR | O_BINARY : O_RDONLY | O_BINARY, 0, &scratch_pathname);
	    }
    #endif

This snippet wants to find `foo.exe' when `foo' is being specified.
Should we add a #define for executable extensions (defaulting to an
empty string on Unix)?


    * symfile.c:symfile_bfd_open()

      /* Look down path for it, allocate 2nd new malloc'd copy.  */
      desc = openp (getenv ("PATH"), 1, name, O_RDONLY | O_BINARY, 0, &absolute_name);
    #if defined(__GO32__) || defined(_WIN32)
      if (desc < 0)
	{
	  char *exename = alloca (strlen (name) + 5);
	  strcat (strcpy (exename, name), ".exe");
	  desc = openp (getenv ("PATH"), 1, exename, O_RDONLY | O_BINARY,
			0, &absolute_name);
	}
    #endif

This is the same issue as in exec.c:exec_file_attach() above, and
should be solved in the same way.