readelf: Add support for printing DW_AT_language_name DW_LNAMEs

readelf: Add support for printing DW_AT_language_name DW_LNAMEs

Add a testfile using GCC 15 (experimental).

	 * libdw/dwarf.h: Add DW_LNAME_lo_user and DW_LNAME_hi_user.
	 * src/readelf.c (dwarf_lname_string): New function.
	 (dwarf_lname_name): Likewise.
	 (attr_callback): Handle DW_AT_language_name by calling
	 dwarf_lname_name.

	 * run-readelf-lnames.sh: New test.
	 * testfile-lnames.bz2: New testfile.
	 * tests/Makefile.am (TESTS): Add run-readelf-lnames.sh.
	 (EXTRA_DIST): Add run-readelf-lnames.sh and
	 testfile-lnames.bz2.

Signed-off-by: Mark Wielaard <mark@klomp.org>