.cxx.o :
$(CC) -c $(CPPFLAGS) -o $@ $<
-VPATH = :$(top_srcdir)/$(program_dir)
+# the comment at the end of the next line is needed because otherwise autoconf
+# would remove this line completely - it contains a built-in hack to remove
+# any VPATH assignment not containing ':'
+VPATH = @PATH_IFS@$(top_srcdir)/$(program_dir) # ':' for autoconf
# Set defaults from configure
include $(top_builddir)/src/make.env