function.
* gold.cc (queue_initial_tasks): Likewise.
(queue_middle_tasks): Likewise.
* object.cc (do_layout): Likewise.
* symtab.cc (is_section_folded): Likewise.
* main.cc (main): Likewise.
* reloc.cc (Read_relocs::run): Likewise.
(Sized_relobj::do_scan_relocs): Likewise.
* icf.cc (is_function_ctor_or_dtor): New function.
(Icf::find_identical_sections): Check if function is ctor or dtor when
safe icf is chosen.
* options.h (General_options::icf): Change option to be an enum.
(Icf_status): New enum.
(icf_enabled): New method.
(icf_safe_folding): New method.
(set_icf_status): New method.
(icf_status_): New variable.
* (options.cc) (General_options::finalize): Set icf_status_.
* testsuite/Makefile.am: Add commands to build icf_safe_test. Modify
icf_test and icf_keep_unique_test to use the --icf enum flag.
* testsuite/icf_safe_test.sh: New file.
* testsuite/icf_safe_test.cc: New file.
