[gold] Recognize DWARF5/GCC5 DW_LANG_Fortran03 and DW_LANG_Fortran08.

[gold] Recognize DWARF5/GCC5 DW_LANG_Fortran03 and DW_LANG_Fortran08.

DWARFv5 defines and GCC5 may output two new DW_LANG constants for the
Fortran 2003 and Fortran 2008 standards. Recognize both in gold gdb-index
as unsupported.

For consistency also add the other new DWARF5/GCC5 language constants in
the elfcpp::DW_LANG enum to match include/dwarf2.h.

elfcpp/ChangeLog:

	* dwarf.h (enum DW_LANG): Add DW_LANG_C_plus_plus_11,
	DW_LANG_C11, DW_LANG_C_plus_plus_14, DW_LANG_Fortran03 and
	DW_LANG_Fortran08 from ../include/dwarf2.h.

gold/ChangeLog:

	* gdb-index.cc (Gdb_index_info_reader::visit_top_die): Recognize
	DW_LANG_Fortran03 and DW_LANG_Fortran08.