[binutils-gdb] Change auto_load_objfile_script_1 to use std::string

[sergiodj+buildbot at sergiodj dot net]

*** TEST RESULTS FOR COMMIT a06ab151cbab6f3da8735d2e5e06ede9454ca4c1 ***

Author: Tom Tromey <tom@tromey.com>
Branch: master
Commit: a06ab151cbab6f3da8735d2e5e06ede9454ca4c1

Change auto_load_objfile_script_1 to use std::string

This replaces some manual string manipulation in
auto_load_objfile_script_1 with std::string, simplifying the code and
allowing the removal of some cleanups.

Tested by the buildbot.

2018-03-17  Tom Tromey  <tom@tromey.com>

	* auto-load.c (auto_load_objfile_script_1): Use std::string.