build: path improvements

Use correct paths in date.py

Fix some build warnings

autogen.sh

@@ -11,16 +11,16 @@ BUILDDIR=build
 
 command -v meson 2> /dev/null
 if [ $? != 0 ]; then
-    echo "*** No meson found, please install it ***"
+    echo "*** 'meson' not found, please install it ***"
     exit 1
 fi
 
 # we could remove build/ but let's avoid rm -rf risks...
 if test -d ${BUILDDIR}; then
-    meson --reconfigure ${BUILDDIR} $@
+    meson setup --reconfigure ${BUILDDIR} $@ || exit 1
 else
-    meson ${BUILDDIR} $@
+    meson setup ${BUILDDIR} $@ || exit 1
 fi
 
-echo "*** Now run 'ninja -C ${BUILDDIR}' to build mu"
-echo "*** Or check the Makefile for some useful targets"
+echo "*** Now run either 'ninja -C ${BUILDDIR}' or 'make' to build mu"
+echo "*** Check the Makefile for other useful targets"