Only relocation handling for now; relaxation is not implemented yet.
bfd/
* elfnn-riscv.c (riscv_elf_check_relocs): Record GOT reference and
paired relocation for TLSDESC_HI20.
(riscv_elf_adjust_dynamic_symbol): Allocate GOT and reloc slots for
TLSDESC symbols.
(riscv_elf_size_dynamic_sections): Likewise but for local symbols.
(tlsdescoff): New helper to determine static addend for R_TLSDESC.
(riscv_elf_relocate_section): Ignore TLSDESC_CALL reloc for now (it is
relaxation only).
Handle TLSDESC_{LOAD,ADD}_LO12 as paired pcrel relocs.
For TLS GOT slot generation, generalize the logic to handle any
combination of (GD, IE, TLSDESC).
Add TLSDESC Rela generation.
* ld/testsuite/ld-riscv-elf/tls*: Add TLSDESC instruction sequences
next to the existing GD and IE sequences. Update expectations.
