toolchain/59390: build with -Wl,-z,pack-relative-relocs by default

[campbell+netbsd%mumble.net@localhost]

>Number:         59390
>Category:       toolchain
>Synopsis:       build with -Wl,-z,pack-relative-relocs by default
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    toolchain-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat May 03 13:30:00 +0000 2025
>Originator:     Taylor R Campbell
>Release:        current
>Organization:
Relocation Relativists LLC
>Environment:
>Description:
Now that ld.elf_so supports packed relative relocations (PR bin/59360: ld.elf_so(8): missing RELR support, https://gnats.NetBSD.org/59360), we should enable it in the build on any platforms where GNU binutils supports it, particularly when MKPIE=yes.  Should be some hefty savings available for some programs:

(amd64)
$ size apropos.{before,after}
   text    data     bss     dec     hex filename
 221781   44930      72  266783   4121f apropos.before
  91637   44978      72  136687   215ef apropos.after
$ size makemandb.{before,after}
   text    data     bss     dec     hex filename
 409881   75868     264  486013   76a7d makemandb.before
 250073   75916     264  326253   4fa6d makemandb.after

Unfortunately, this is blocked on CTF tool support for RELR (PR toolchain/59364: ctf tools needs update, https://gnats.NetBSD.org/59364):

ERROR: nbctfmerge: apropos: Cannot get sect .relr.dyn data: Invalid section descriptor
>How-To-Repeat:
binary inspetion
>Fix:
Yes, please!