lto-wrapper: Pass through -funwind-tables and -fasynchronous-unwind-tables

The -funwind-tables and -fasynchronous-unwind-tables options are relevant
for the output pass, so they need to be passed through by the LTO wrapper.
Otherwise, dwarf2out_assembly_start may output a ".cfi_sections
.debug_frame" directive when debug info is enabled even if every
translation unit was compiled with -funwind-tables.

gcc/
	* lto-wrapper.cc (merge_and_complain): Handle
	-funwind-tables and -fasynchronous-unwind-tables.
	(append_compiler_options): Likewise.