Enable arm64 .eh_frame terminator, align it to 4

Every architecture that uses .eh_frame needs a terminator at the end to
ensure that an unwinder library doesn't read past the end of the
section. This can happen when the unwinder looks up a PC that doesn't
have a matching FDE. Both LLVM libunwind and libgcc fall back to an
.eh_frame scan if the .eh_frame_hdr search table scan fails.

By convention, this terminator section is aligned to 4, even on 64-bit
targets. e.g. Both libgcc and compiler-rt have a crtend with 4-byte
.eh_frame alignment on arm64 and x86_64.

In practice, lld strips off the terminator from input object files and
adds one unconditionally to the output, but bfd/gold still require a
crtend with a terminator.

References:
 - https://reviews.llvm.org/D86256
 - https://reviews.llvm.org/D87750
 - https://sourceware.org/bugzilla/show_bug.cgi?id=2655

Test: examine crtend.o and crtend_so.o with `readelf -SW` and \
  `objdump -Wf`
Change-Id: Ib8478ee446ad806898aa7147a6208d384c7516d5

0 files changed, 0 insertions, 0 deletions