RISC-V: Don't separate pcgp relaxation to another relax pass.

RISC-V: Don't separate pcgp relaxation to another relax pass.

Commit abd20cb637008da9d32018b4b03973e119388a0a and
ebdcad3fddf6ec21f6d4dcc702379a12718cf0c4 introduced additional
complexity into the paths run by the RISC-V relaxation pass in order to
resolve the issue of accurately keeping track of pcrel_hi and pcrel_lo
pairs. The first commit split up relaxation of these relocs into a pass
which occurred after other relaxations in order to prevent the situation
where bytes were deleted in between a pcrel_lo/pcrel_hi pair, inhibiting
our ability to find the corresponding pcrel_hi relocation from the
address attached to the pcrel_lo.

Since the relaxation was split into two passes the 'again' parameter
could not be used to perform the entire relaxation process again and so
the second commit added a way to restart ldelf_map_segments, thus
starting the whole process again.

Unfortunately this process could not account for the fact that we were
not finished with the relaxation process so in some cases - such as the
case where code would not fit in a memory region before the
R_RISCV_ALIGN relocation was relaxed - sanity checks in generic code
would fail.

This patch fixes all three of these concerns by reverting back to a
system of having only one target relax pass but updating entries in the
table of pcrel_hi/pcrel_lo relocs every time any bytes are deleted. Thus
we can keep track of the pairs accurately, and we can use the 'again'
parameter to restart the entire target relax pass, behaving in the way
that generic code expects. Unfortunately we must still have an
additional pass to delay deleting AUIPC bytes to avoid ambiguity between
pcrel_hi relocs stored in the table after deletion. This pass can only
be run once so we may potentially miss out on relaxation opportunities
but this is likely to be rare.

https://sourceware.org/bugzilla/show_bug.cgi?id=28410

bfd/
	* elfnn-riscv.c (riscv_elf_link_hash_table): Removed restart_relax.
	(riscv_elf_link_hash_table_create): Updated.
	(riscv_relax_delete_bytes): Moved after the riscv_update_pcgp_relocs.
	Update the pcgp_relocs table whenever bytes are deleted.
	(riscv_update_pcgp_relocs): Add function to update the section
	offset of pcrel_hi and pcrel_lo, and also update the symbol value
	of pcrel_hi.
	(_bfd_riscv_relax_call): Need to update the pcgp_relocs table
	when deleting codes.
	(_bfd_riscv_relax_lui): Likewise.
	(_bfd_riscv_relax_tls_le): Likewise.
	(_bfd_riscv_relax_align): Once we've handled an R_RISCV_ALIGN,
	we can't relax anything else, so set the sec->sec_flg0 to true.
	Besides, we don't need to update the pcgp_relocs table at this
	stage, so just pass NULL pointer as the pcgp_relocs table for
	riscv_relax_delete_bytes.
	(_bfd_riscv_relax_section): Use only one pass for all target
	relaxations.
	(_bfd_riscv_relax_delete): Likewise, we don't need to update
	the pcgp_relocs table at this stage, and don't need to set
	the `again' since restart_relax mechanism is abandoned.
	(bfd_elfNN_riscv_restart_relax_sections): Removed.
	(_bfd_riscv_relax_section): Updated.
	* elfxx-riscv.h (bfd_elf32_riscv_restart_relax_sections): Removed.
	(bfd_elf64_riscv_restart_relax_sections): Likewise.
ld/
	* emultempl/riscvelf.em: Revert restart_relax changes and set
	relax_pass to 3.
	* testsuite/ld-riscv-elf/align-small-region.d: New testcase.
	* testsuite/ld-riscv-elf/align-small-region.ld: Likewise.
	* testsuite/ld-riscv-elf/align-small-region.s: Likewise.
	* testsuite/ld-riscv-elf/restart-relax.d: Removed sine the
	restart_relax mechanism is abandoned.
	* testsuite/ld-riscv-elf/restart-relax.s: Likewise.
	* testsuite/ld-riscv-elf/ld-riscv-elf.exp: Updated.