updated for version 7.3.1221
Problem:    When build flags change "make distclean" run into a configure
            error.
Solution:   When CFLAGS changes delete auto/config.cache.  Also avoid adding
            duplicate text to flags.
diff --git a/src/Makefile b/src/Makefile
index 39e0e32..39bcbd2 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -1655,6 +1655,11 @@
 # sure configure is run when it's needed.
 #
 config auto/config.mk: auto/configure config.mk.in config.h.in
+	if test -f auto/config.cache && \
+	    grep '^ac_cv_env_CFLAGS_value=' auto/config.cache > /dev/null && \
+	    ! grep -x -F 'ac_cv_env_CFLAGS_value=$(CFLAGS)' auto/config.cache > /dev/null; then \
+		rm auto/config.cache; \
+	fi
 	GUI_INC_LOC="$(GUI_INC_LOC)" GUI_LIB_LOC="$(GUI_LIB_LOC)" \
 		CC="$(CC)" CPPFLAGS="$(CPPFLAGS)" CFLAGS="$(CFLAGS)" \
 		LDFLAGS="$(LDFLAGS)" $(CONF_SHELL) srcdir="$(srcdir)" \