Dropped use of depricated python3-setuptools / distutils.

Make sure sysconfig.get_path("platlib") return correct path on Debian
and Ubuntu systems, where /usr/lib/ should be used over
/usr/local/lib.

Based on e2c10a8 by Andy Pugh and
pull request LinuxCNC#3155 by Eckeneckepen.

Fixes Debian issue #1080668.

debian/rules.in

@@ -44,7 +44,11 @@ export PYTHON=/usr/bin/python3
 
 override_dh_auto_configure:
 	cd src && ./autogen.sh
-	cd src && ./configure \
+# Setting DEB_PYTHON_INSTALL_LAYOUT adjust sysconfig 'platlib' path,
+# see <URL: https://bugs.debian.org/1080668 >.  This affect
+# configure.ac settings for SITEPY and might also affect AX_PYTHON and
+# AX_PYTHON_DEVEL.
+	cd src && DEB_PYTHON_INSTALL_LAYOUT=deb ./configure \
 	    --prefix=/usr --sysconfdir=/etc \
 	    --mandir=/usr/share/man \
 	    $(configure_realtime_arg) \

src/configure.ac

@@ -1684,7 +1684,7 @@ fi
 AC_MSG_RESULT([$PYTHON_TK_VERSION])
 
 AC_MSG_CHECKING(for site-package location)
-SITEPY=`$PYTHON -c 'import distutils.sysconfig; print(distutils.sysconfig.get_python_lib())'`
+SITEPY="$($PYTHON -c 'import sysconfig; s = sysconfig.get_scheme_names(); m=list(set(("deb_system", "rpm_prefix")) & set(s)); print(sysconfig.get_path("platlib")) if m else print("/usr/lib/python3/dist-packages");')"
 AC_MSG_RESULT($SITEPY)
 
 AC_MSG_CHECKING(for working GLU quadrics)

src/m4/ax_python.m4

@@ -64,7 +64,7 @@ if test x$ax_python_bin != x; then
      AC_CHECK_LIB(${ax_python_bin}m, main, ax_python_lib=${ax_python_bin}m, ax_python_lib=no)
    fi
    if test x$ax_python_lib != xno; then
-     ax_python_header=`$ax_python_bin -c "from distutils.sysconfig import *; print(get_config_var('CONFINCLUDEPY'))"`
+     ax_python_header=`$ax_python_bin -c "import sysconfig; print(sysconfig.get_path('include'))"`
      if test x$ax_python_header != x; then
        break;
      fi

src/m4/ax_python_devel.m4

@@ -188,31 +188,19 @@ variable to configure. See ``configure --help'' for reference.
 
 	if test $ax_python_devel_found = yes; then
 	   #
-	   # Check if you have distutils, else fail
+	   # Check if you have sysconfig, else fail
 	   #
 	   AC_MSG_CHECKING([for the sysconfig Python package])
 	   ac_sysconfig_result=`$PYTHON -c "import sysconfig" 2>&1`
 	   if test $? -eq 0; then
 		AC_MSG_RESULT([yes])
 		IMPORT_SYSCONFIG="import sysconfig"
 	   else
-		AC_MSG_RESULT([no])
-
-		AC_MSG_CHECKING([for the distutils Python package])
-		ac_sysconfig_result=`$PYTHON -c "from distutils import sysconfig" 2>&1`
-		if test $? -eq 0; then
-			AC_MSG_RESULT([yes])
-			IMPORT_SYSCONFIG="from distutils import sysconfig"
-		else
-			AC_MSG_WARN([cannot import Python module "distutils".
+			ax_python_devel_found=no
+			AC_MSG_ERROR([cannot import Python module "sysconfig".
 Please check your Python installation. The error was:
 $ac_sysconfig_result])
-			if ! $ax_python_devel_optional; then
-			   AC_MSG_ERROR([Giving up])
-			fi
-			ax_python_devel_found=no
 			PYTHON_VERSION=""
-		fi
 	   fi
 	fi
 
@@ -228,12 +216,6 @@ $ac_sysconfig_result])
 				print (sysconfig.get_path ('include'));"`
 			plat_python_path=`$PYTHON -c "$IMPORT_SYSCONFIG; \
 				print (sysconfig.get_path ('platinclude'));"`
-		else
-			# old distutils way
-			python_path=`$PYTHON -c "$IMPORT_SYSCONFIG; \
-				print (sysconfig.get_python_inc ());"`
-			plat_python_path=`$PYTHON -c "$IMPORT_SYSCONFIG; \
-				print (sysconfig.get_python_inc (plat_specific=1));"`
 		fi
 		if test -n "${python_path}"; then
 			if test "${plat_python_path}" != "${python_path}"; then