[PATCH 0 of 1 v10] [PATCH 0 of 1] aarch64: add PAC and BTI Support]

[Bill Roberts]

Hello,

This is a resend of the resend... The patches are rebased onto the current tip:
  - https://gmplib.org/list-archives/gmp-devel/2025-November/006330.html
  - https://gmplib.org/list-archives/gmp-devel/2026-July/006466.html

The FSF agreement is complete, so hopefully this will just be a technical
review and maybe even a merge. It would be nice to get this to land, since
it's a core component of userspace and Fedora builds C and C++ userspace
with PAC and BTI enabled, this gets pulled into a lot of things, it would
be nice to close this.

See Commit Message for More Details

-V10:
  - Fix copyright update

- V9:
  - drop the separate patches in the series using AC_PROG_SED|GREP
  - use env vars for the test script
  - make the test skip if readelf is not available for the test
  - Make the test script POSIX shell only

- V8:
  - fix commit message: "echo message | sed -i s/sed/grep"

- V7:
  - Drop GMP_GET_MACRO_VALUE
  - Drop GMP_CHECK_PROG
  - configure.ac already uses sed and grep, hardcoded, so add checks for them
    and use the variables over the direct command
  - Bolster documentation with links to the Arm ARM, ABI and Blog documentations
    - Make some clarifications in the commit message as well
  - Add NONLEAF_PROLOGUE instead of calling PROLOGUE(xxx, true)
    - naming convention follows MULFUNC_PROLOGUE naming convention
    - Update the pattern matching for determining if generic C or asm should be used
    - Requires EGREP for automatic configuration of assembly routines over generic
      C implementations
  - Add License to t-arm64_elf_check.sh
  - Detect sed and grep using autoconf and use the proper SED and GREP variables
    respectively to invoke them vs hardcoding it
  - Drop erroneous Makefile.am formatting change

- V6:
  - Fix commit message wording
  - Fix double use of sign in commit message when verify was intended
  - Drop spurious whitespace only change in configure.ac
  - comment in tests/mpn/t-arm64_bti.c why we return 0 if the symbol is not found
  - Fix table whitespace in tests/mpn/t-arm64_bti.c
  - Use declare -g over eval in tests/mpn/t-arm64_elf_check.sh
  - Quote rc calculation and exit in tests/mpn/t-arm64_elf_check.sh
  - Fix typo in tests/mpn/t-arm64_elf_check.sh "binary ast he ONLY" -> "binary as the ONLY"
 
- V5:
  - Fix cross compilation support
- V4:
  - Fix typos in bash script comments
- V3:
  - Use divert(1) to add GNU Notes to ELF files to avoid
    needing the macro in each file.
- V2:
  - Add tests
- V1:
  - Initial Commit