[RISCV] Recognize new relocation types

[PkmX]

Summary

These new relocation types were taken from latest RISC-V binutils.

They are needed by the RISC-V port of lld which we plan to upstream, so we figured we should let this change land in llvm first.

[asb]

Many thanks, R_RISCV_32_PCREL isn't currently documented in the riscv-elf-psabi-doc, but it seems was applied to upstream binutils. Looks good to me.

[asb]

I've committed this patch for you, after verifying R_RISCV_32_PCREL has been included in a release binutils (and therefore can be considered "final" despite not being documented). I've made an issue on the riscv-elf-psabi-doc for documenting this relocation https://github.com/riscv/riscv-elf-psabi-doc/issues/36. Thanks again.

llvm/trunk/include/llvm/BinaryFormat/ELFRelocs/RISCV.def

 ELF_RELOC(R_RISCV_GNU_VTINHERIT,     41)
 ELF_RELOC(R_RISCV_GNU_VTENTRY,       42)
 ELF_RELOC(R_RISCV_ALIGN,             43)
 ELF_RELOC(R_RISCV_RVC_BRANCH,        44)
 ELF_RELOC(R_RISCV_RVC_JUMP,          45)
 ELF_RELOC(R_RISCV_RVC_LUI,           46)
 ELF_RELOC(R_RISCV_GPREL_I,           47)
 ELF_RELOC(R_RISCV_GPREL_S,           48)
+ELF_RELOC(R_RISCV_TPREL_I,           49)
+ELF_RELOC(R_RISCV_TPREL_S,           50)
+ELF_RELOC(R_RISCV_RELAX,             51)
+ELF_RELOC(R_RISCV_SUB6,              52)
+ELF_RELOC(R_RISCV_SET6,              53)
+ELF_RELOC(R_RISCV_SET8,              54)
+ELF_RELOC(R_RISCV_SET16,             55)
+ELF_RELOC(R_RISCV_SET32,             56)
+ELF_RELOC(R_RISCV_32_PCREL,          57)