libelf, readelf, elflint: Add RELR support

libelf, readelf, elflint: Add RELR support

Handle RELR as defined here:
https://groups.google.com/g/generic-abi/c/bX460iggiKg/m/YT2RrjpMAwAJ

Introduce new ELF_T_RELR Elf_Type and handle it for SHT_RELR.  Check
various properties in elflint.  Print RELR relocations in
readelf. Just the entries with -U.  Just the addresses with -N. And
addresses plus symbol/offsets by default.

Also add a test to check that gelf.h works with the system elf.h.

	* libebl/eblsectiontypename.c (ebl_section_type_name): Add RELR
	to knownstype.
	* libelf/elf32_updatenull.c (updatenull_wrlock): Handle
	sh_entsize for SHT_RELR.
	* libelf/gelf.h (GElf_Relr): New typedef for Elf64_Relr.
	* libelf/gelf_fsize.c (__libelf_type_sizes): Add ELF_T_RELR.
	* libelf/gelf_xlate.c (__elf_xfctstom): Likewise.
	* libelf/gelf_xlate.h: Add RELR as FUNDAMENTAL.
	* libelf/libelf.h (Elf_Type): Add ELF_T_RELR. Add RELR
	defines/typedefs if undefined in system elf.h.
	* libelf/libelfP.h: Define ELF32_FSZ_RELR and ELF64_FSZ_RELR.
	* src/elflint.c (check_reloc_shdr): Check she_entsize for
	ELF_T_RELR.
	(check_relr): New function.
	(check_dynamic): Handle DT_RELR.
	(special_sections): Add SHT_RELR.
	(check_sections): Call check_relr.
	* src/readelf.c (print_relocs): Also accept a Dwfl_Module.
	(handle_relocs_relr): New function.
	(print_dwarf_addr): Make static and declare early.
	(process_elf_file): Pass dwflmod to print_relocs.
	(handle_dynamic): Handle DT_RELRSZ and DTRELRENT.
	* system-elf-gelf-test.c: New test.
	* Makefile.am (TESTS): Add system-elf-gelf-test.
	(check_PROGRAMS): Likewise.
	(system_elf_gelf_test_CPPFLAGS): New variable.
	(system_elf_gelf_test_LDADD): Likewise.

https://sourceware.org/bugzilla/show_bug.cgi?id=28495

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