readelf: Support SHT_RELR/DT_RELR for -r
The -r output for SHT_RELR looks like:
Relocation section '.relr.dyn' at offset 0x530 contains 4 entries:
7 offsets
00000000000028c0
00000000000028c8
0000000000003ad0
0000000000003ad8
0000000000003ae0
0000000000003ae8
0000000000003af0
For --use-dynamic, the header looks like
'RELR' relocation section at offset 0x530 contains 32 bytes:
include/
* elf/common.h (DT_ENCODING): Bump to 38.
* elf/external.h (Elf32_External_Relr): New.
(Elf64_External_Relr): New.
(cherry picked from commit
a7fd11862703e45d2774981a4888bc127d473b06)