Fix diffutils build breakage with BR2_STRIP_none=y

Look at BR2_STRIP_none to decide whether to strip diffutils binaries.
This avoids bad quoting in diffutils Makefile.in (generated by automake 1.6)
when STRIP is set to:   true -Not_stripping

Signed-off-by:  Marc Gauthier <marc@alumni.uwaterloo.ca>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/diffutils/diffutils.mk

@@ -94,7 +94,8 @@ $(DIFFUTILS_DIR)/$(DIFFUTILS_BINARY): $(DIFFUTILS_DIR)/.configured
 	$(MAKE) CC=$(TARGET_CC) -C $(DIFFUTILS_DIR)
 
 $(TARGET_DIR)/$(DIFFUTILS_TARGET_BINARY): $(DIFFUTILS_DIR)/$(DIFFUTILS_BINARY)
-	$(MAKE) DESTDIR=$(TARGET_DIR) CC=$(TARGET_CC) -C $(DIFFUTILS_DIR) install-strip
+	$(MAKE) DESTDIR=$(TARGET_DIR) CC=$(TARGET_CC) -C $(DIFFUTILS_DIR) \
+		$(if $(BR2_STRIP_none),install,install-strip)
 ifneq ($(BR2_HAVE_INFOPAGES),y)
 	rm -rf $(TARGET_DIR)/usr/share/info
 endif