Move libspl_assertf into .c file

Variadic functions cannot be inlined. libspl_assertf ends up being
duplicated in every file that uses it.

Fix this by moving the function into a new assert.c. Also move the
definition of aok into the new file instead of zone.c.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Closes #10538

tests/zfs-tests/tests/functional/checksum/Makefile.am

@@ -1,7 +1,9 @@
 include $(top_srcdir)/config/Rules.am
 
 AM_CPPFLAGS += -I$(top_srcdir)/include
-LDADD = $(top_builddir)/lib/libicp/libicp.la
+LDADD = \
+	$(top_builddir)/lib/libicp/libicp.la \
+	$(top_builddir)/lib/libspl/libspl_assert.la
 
 AUTOMAKE_OPTIONS = subdir-objects
 

tests/zfs-tests/tests/functional/checksum/edonr_test.c

@@ -40,8 +40,6 @@
 #include <sys/time.h>
 #include <sys/stdtypes.h>
 
-int aok = 0;
-
 /*
  * Test messages from:
  * http://csrc.nist.gov/groups/ST/toolkit/documents/Examples/SHA_All.pdf