[PATCH 0/4] alpha: add IFUNC support

[Matt Turner]

Testing this series against glibc turned up a case it got wrong, so I have
sent v2 of two of the four patches, each in reply to the patch it replaces:

  [PATCH v2 2/4] alpha: resolve IFUNCs this link resolves itself out of
                 .rela.iplt
  [PATCH v2 4/4] alpha: handle IFUNC symbols with local binding

1/4 and 3/4 are unchanged.  3/4 still applies on top of v2 2/4; only its
hunk offsets move.

An IFUNC referenced from a non-PIE executable killed the linker:

  BFD assertion fail bfd/elf64-alpha.c:4216
  collect2: fatal error: ld terminated with signal 11 [Segmentation fault]

Such an IFUNC cannot be preempted, so it never becomes a dynamic symbol
and the sizing code reserves nothing for it in .rela.got or .rela.<sec>.
check_relocs knew that and reserved .rela.iplt space instead, but
relocate_section decided where to emit by asking whether the link had
dynamic sections at all, and so took the ordinary path and was handed the
dynamic reloc section for the input section, which is a null pointer
because nothing ever created one.

v2 2/4 makes both sides ask the same question -- does this link resolve
the IFUNC itself, which is so both when there is no dynamic linker and
when the link is not position-independent.  It also sizes the .rela.iplt
space for such a symbol's GOT entries in a dynamic link, which only the
static path did before, and skips a symbol with a PLT entry in both the
sizing and the emitting, since finish_dynamic_symbol handles those and
.rela.iplt would otherwise overrun.

Because the fix belongs where the mistake was, I folded it into 2/4 rather
than adding a fifth patch: without it, 2/4 and 3/4 segfault the linker on
an ordinary non-PIE executable, which is unpleasant to bisect through.
2/4 is retitled, since it no longer only concerns static links.

Each patch builds on its own, and check-ld at the tip of the series has no
unexpected failures.  New tests cover a dynamic executable that references
and calls an IFUNC, with local and with global binding; both fail without
this change.

With the series applied, glibc builds on alpha with --enable-multi-arch
and its IFUNC tests link, where before six of them did not.

Thanks,
Matt