Correct a flaw in the Python 3 version checking

It turns out the ax_python_devel.m4 version check assumes that
("3.X+1.0" >= "3.X.0") is True in Python, which is not when X+1
is 10 or above and X is not. (Also presumably X+1=100 and ...)

So let's remake the check to behave consistently, using the
"packaging" or (if absent) the "distlib" modules.

Signed-off-by: Rich Ercolani <rincebrain@gmail.com>

config/always-pyzfs.m4

@@ -46,6 +46,21 @@ AC_DEFUN([ZFS_AC_CONFIG_ALWAYS_PYZFS], [
 	])
 	AC_SUBST(DEFINE_PYZFS)
 
+	dnl #
+	dnl # Python "packaging" (or, failing that, "distlib") module is required to build and install pyzfs
+	dnl #
+	AS_IF([test "x$enable_pyzfs" = xcheck -o "x$enable_pyzfs" = xyes], [
+		ZFS_AC_PYTHON_MODULE([packaging], [], [
+			ZFS_AC_PYTHON_MODULE([distlib], [], [
+				AS_IF([test "x$enable_pyzfs" = xyes], [
+					AC_MSG_ERROR("Python $PYTHON_VERSION packaging and distlib modules are not installed")
+				], [test "x$enable_pyzfs" != xno], [
+					enable_pyzfs=no
+				])
+			])
+		])
+	])
+
 	dnl #
 	dnl # Require python-devel libraries
 	dnl #

config/ax_python_devel.m4

@@ -97,9 +97,18 @@ AC_DEFUN([AX_PYTHON_DEVEL],[
 	# Check for a version of Python >= 2.1.0
 	#
 	AC_MSG_CHECKING([for a version of Python >= '2.1.0'])
-	ac_supports_python_ver=`$PYTHON -c "import sys; \
-		ver = sys.version.split ()[[0]]; \
-		print (ver >= '2.1.0')"`
+	ac_supports_python_ver=`cat<<EOD | $PYTHON -
+from __future__ import print_function;
+import sys;
+try:
+	from packaging import version;
+except ImportError:
+	from distlib import version;
+ver = sys.version.split ()[[0]];
+(tst_cmp,tst_ver) = ">= '2.1.0'".split ();
+tst_ver = tst_ver.strip ("'");
+eval ("print (version.LegacyVersion (ver)"+ tst_cmp +"version.LegacyVersion (tst_ver))")
+EOD`
 	if test "$ac_supports_python_ver" != "True"; then
 		if test -z "$PYTHON_NOVERSIONCHECK"; then
 			AC_MSG_RESULT([no])
@@ -126,9 +135,21 @@ to something else than an empty string.
 	#
 	if test -n "$1"; then
 		AC_MSG_CHECKING([for a version of Python $1])
-		ac_supports_python_ver=`$PYTHON -c "import sys; \
-			ver = sys.version.split ()[[0]]; \
-			print (ver $1)"`
+		# Why the strip ()?  Because if we don't, version.parse
+		# will, for example, report 3.10.0 >= '3.11.0'
+		ac_supports_python_ver=`cat<<EOD | $PYTHON -
+
+from __future__ import print_function;
+import sys;
+try:
+	from packaging import version;
+except ImportError:
+	from distlib import version;
+ver = sys.version.split ()[[0]];
+(tst_cmp,tst_ver) = "$1".split ();
+tst_ver = tst_ver.strip ("'");
+eval ("print (version.LegacyVersion (ver)"+ tst_cmp +"version.LegacyVersion (tst_ver))")
+EOD`
 		if test "$ac_supports_python_ver" = "True"; then
 		   AC_MSG_RESULT([yes])
 		else