Add use of libabigail for ABI checks

[bregma]

Added make -C src check-abi target to leverage libabigail 2.0 tools to check for ABI changes.

Add ABI baseline files for aarch64, i686, riscv, s390x, and x86_64 Linux targets and aarch64 and x86_64 QNX SDP 7.1 targets.

Used the check-abi target in the CI-unix github workflow.

[bregma]

Found a better, more elegant way to generate and process the ABI files by using make rules instead of shell scripting.

[bertwesarg]

Found a better, more elegant way to generate and process the ABI files by using make rules instead of shell scripting.

nice. just in case you want a custom prefix instead of the generic GEN. put something like this into your Makefile.am:

UNW_V_ABIDW = $(unw__v_ABIDW_@AM_V@)
unw__v_ABIDW_ = $(unw__v_ABIDW_@AM_DEFAULT_V@)
unw__v_ABIDW_0 = @echo "  ABIDW    $@";
unw__v_ABIDW_1 =
UNW_V_ABIDIFF = $(unw__v_ABIDIFF_@AM_V@)
unw__v_ABIDIFF_ = $(unw__v_ABIDIFF_@AM_DEFAULT_V@)
unw__v_ABIDIFF_0 = @echo "  ABIDIFF  $@";
unw__v_ABIDIFF_1 =

and use $(UNW_V_ABIDW) and $(UNW_V_ABIDIFF)

[bregma]

The archived ABI files need to be generated against a build configured with --enable-debug because that configuration flag changes the ABI and it's used in CI. Maybe there should be two sets of archived ABI files, one for with --enable-debug and one for without?

[bertwesarg]

LGTM