Recognize new DWARF5/GCC5 DW_LANG Fortran 2003 and Fortran 2008 standards.

DWARFv5 defines and GCC5 may output two new DW_LANG constants for the
Fortran 2003 and Fortran 2008 standards. Recognize both as variants of
language_fortran.

gdb/ChangeLog:

	* dwarf2read.c (set_cu_language): Recognize DW_LANG_Fortran03 and
	DW_LANG_Fortran08 as language_fortran.

http://dwarfstd.org/ShowIssue.php?issue=141121.1