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_core/Makefile.am

@@ -1,9 +1,12 @@
 include $(top_srcdir)/config/Rules.am
+PHONY =
 
 pkgconfig_DATA = libzfs_core.pc
 
 lib_LTLIBRARIES = libzfs_core.la
 
+include $(top_srcdir)/config/Abigail.am
+
 USER_C = \
 	libzfs_core.c
 

lib/libzfs_core/libzfs_core.suppr

@@ -0,0 +1,5 @@
+[suppress_type]
+	name = FILE*
+
+[suppress_type]
+	name = pthread_cond_t