dwarf_lang_to_enum_language: Map new DWARF5 constants

Add new DWARF5 language codes to gdb/dwarf2/read.c where
they are converted to GDB language names. The codes
were added to include/dwarf.h by syncing with gcc, Ada language
codes were added to dwarf.h earlier.

Approved-By: Tom Tromey <tom@tromey.com>
Approved-By: Andrew Burgess <aburgess@redhat.com>