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

lib/libzfs/Makefile.am

@@ -1,4 +1,5 @@
 include $(top_srcdir)/config/Rules.am
+PHONY =
 
 VPATH = \
 	$(top_srcdir)/module/icp \
@@ -13,6 +14,8 @@ pkgconfig_DATA = libzfs.pc
 
 lib_LTLIBRARIES = libzfs.la
 
+include $(top_srcdir)/config/Abigail.am
+
 USER_C = \
 	libzfs_changelist.c \
 	libzfs_config.c \

lib/libzfs/libzfs.suppr

@@ -0,0 +1,13 @@
+[suppress_type]
+	name = FILE*
+
+[suppress_type]
+	type_kind = typedef
+	name = SHA256_CTX
+
+[suppress_type]
+	type_kind = typedef
+	name = SHA2_CTX
+
+[suppress_variable]
+	name = zfs_deleg_perm_tab