lld: add -z interpose support

[emaste]

Summary

-z interpose sets the DF_1_INTERPOSE flag, marking the object as an interposer.

PR:             230604
Reported by:    jbeich
Sponsored by:   The FreeBSD Foundation

[emaste]

I will add an automated test case and submit this upstream shortly, but would like to get this sorted out in advance of 12.0's branch.

-z interpose sets DF_1_INTERPOSE in DT_FLAGS_1 as expected:

Dynamic section at offset 0x3028 contains 22 entries:
  Tag        Type                         Name/Value
 0x0000000000000001 (NEEDED)             Shared library: [libc.so.7]
 0x000000006ffffffb (FLAGS_1)            Flags: INTERPOSE
...

I did find that ELF Tool Chain readelf does not decode DT_FLAGS_1 though:

Dynamic section at offset 0x3028 contains 22 entries:
  Tag                Type                  Name/Value
 0x0000000000000001 NEEDED               Shared library: [libc.so.7]
 0x000000006ffffffb FLAGS_1             
...

[emaste]

Upstream review: https://reviews.llvm.org/D52094

[emaste]

Upstream commit: https://reviews.llvm.org/rL342239

[emaste]

typo from @markj

[markj]

usr.bin/clang/lld/ld.lld.1

456 ↗

(On Diff #48048)

"indicate"

457 ↗

(On Diff #48048)

I'd put a comma after "application," but that's just me.

[emaste]

upload correct patch

[emaste]

more commas