RISC-V: Use pc-relative relocation for FDE initial location

The symbol address in .eh_frame may be adjusted in
_bfd_elf_discard_section_eh_frame, and the content of .eh_frame will be
adjusted in _bfd_elf_write_section_eh_frame. Therefore, we cannot insert
a relocation whose addend symbol is in .eh_frame. Othrewise, the value
may be adjusted twice.

bfd/ChangeLog
2017-06-26  Kuan-Lin Chen  <rufus@andestech.com>

	* elfnn-riscv.c (perform_relocation): Support the new
	R_RISCV_32_PCREL relocation.
	(riscv_elf_relocate_section): Likewise.
	* elfxx-riscv.c (howto_table): Likewise.
	(riscv_reloc_map): Likewise.
	* bfd-in2.h (BFD_RELOC_RISCV_32_PCREL): New relocation.
	* libbfd.h: Regenerate.

gas/ChangeLog
2017-06-26  Kuan-Lin Chen  <rufus@andestech.com>

	* config/tc-riscv.c (md_apply_fix) [BFD_RELOC_32]: Convert to a
	R_RISCV_32_PCREL relocation.

include/ChangeLog
2017-06-26  Kuan-Lin Chen  <rufus@andestech.com>

	* elf/riscv.h (R_RISCV_32_PCREL): New.