Merge #1649

1649: dwarf2out.c: Don't emit DW_LANG_Rust_old r=dkm a=dkm

DW_LANG_Rust_old is a non-standard DWARF language code used by old rustc compilers before DWARF5 (released in 2017). Just always emit DW_LANG_Rust unless producing strict DWARF for versions before 5. And in that old strict DWARF case just emit DW_LANG_C instead of a non-standard language code.

Co-authored-by: Mark Wielaard <mark@klomp.org>

diff --cc gcc/dwarf2out.cc
Simple merge