RISC-V: Fix weak function call reloc overflow on llvm build.

RISC-V: Fix weak function call reloc overflow on llvm build.

	bfd/
	PR 25205
	* elfnn-riscv.c (riscv_elf_relocate_section) <R_RISCV_CALL>: Add
	check for !bfd_link_pic (info).
	<R_RISCV_CALL_PLT>: Move next to R_RISCV_CALL.
	<R_RISCV_JAL>: Add comment.
	(_bfd_riscv_relax_section): For plt.offset check, add check for
	bfd_link_pic (info).  Add comment.

Change-Id: Ie769bc3d5adf096a51df5cc12efe3d50e80acb8f