Library ABI tracking with abigail

Provide two make targets: checkabi and storeabi.

storeabi uses libabigail to generate a reference copy of the ABI for the
public libraries.

checkabi compares such a reference to the compiled version, failing if
they are not compatible.  No ABI is generated for libzpool.so, it is
only used by ztest and zdb and not external consumers.

Co-authored-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Antonio Russo <aerusso@aerusso.net>
Closes #11144

config/Abigail.am

@@ -0,0 +1,29 @@
+#
+# When performing an ABI check the following options are applied:
+#
+# --no-unreferenced-symbols: Exclude symbols which are not referenced by
+# any debug information.  Without this _init() and _fini() are incorrectly
+# reported on CentOS7 for libuutil.so.
+#
+# --headers-dir1: Limit ABI checks to public OpenZFS headers, otherwise
+# changes in public system headers are also reported.
+#
+# --suppressions: Honor a suppressions file for each library to provide
+# a mechanism for suppressing harmless warnings.
+#
+
+PHONY += checkabi storeabi
+
+checkabi:
+	for lib in $(lib_LTLIBRARIES) ; do \
+		abidiff --no-unreferenced-symbols \
+		    --headers-dir1 ../../include \
+		    --suppressions $${lib%.la}.suppr \
+		    $${lib%.la}.abi .libs/$${lib%.la}.so ; \
+	done
+
+storeabi:
+	cd .libs ; \
+	for lib in $(lib_LTLIBRARIES) ; do \
+		abidw $${lib%.la}.so > ../$${lib%.la}.abi ; \
+	done