backends: Add x86_64 section_type_name for SHT_X86_64_UNWIND.

Makes sure that eu-readelf and eu-elflint recognize and show the
x86_64 specific section type correctly.

Signed-off-by: Mark Wielaard <mark@klomp.org>
Tested-by: Milian Wolff <milian.wolff@kdab.com>
3 files changed