RISC-V: Relax R_RISCV_[PCREL_]LO12_I/S to R_RISCV_GPREL_I/S for undefined weak.

RISC-V: Relax R_RISCV_[PCREL_]LO12_I/S to R_RISCV_GPREL_I/S for undefined weak.

bfd/
	*elfnn-riscv.c (_bfd_riscv_relax_lui): For undefined weak symbol,
	just relax the R_RISCV_LO12_I/S to R_RISCV_GPREL_I/S, and then don't
	update the rs1 to zero until relocate_section.
	(_bfd_riscv_relax_pc): Likewise, but for R_RISCV_PCREL_LO12_I/S.