build: fix the toolchain rebuild check

- Check for changes in toolchain/ only
- Only replace the stamp file if it was changed
- Fix dependencies for staging dir prepare
- Move the stamp file to TOOLCHAIN_DIR

Signed-off-by: Felix Fietkau <nbd@nbd.name>

toolchain/Makefile

@@ -70,15 +70,15 @@ endif
 endif
 
 ifdef CONFIG_BUILDBOT
-  $(STAGING_DIR)/.toolchain_ver_check: $(TMP_DIR)/.build
-	cd "$(TOPDIR)"; git log --format=%h -1 > $(TMP_DIR)/.toolchain_ver_check
-	cmp -s $(TMP_DIR)/.toolchain_ver_check $@ || \
-		rm -rf $(BUILD_DIR) $(STAGING_DIR) $(TOOLCHAIN_DIR) $(BUILD_DIR_TOOLCHAIN)
-	mkdir -p $(STAGING_DIR)
-	mv $(TMP_DIR)/.toolchain_ver_check $@
+  $(TOOLCHAIN_DIR)/stamp/.ver_check: $(TMP_DIR)/.build
+	cd "$(TOPDIR)"; git log --format=%h -1 toolchain > $(TMP_DIR)/.ver_check
+	cmp -s $(TMP_DIR)/.ver_check $@ || { \
+		rm -rf $(BUILD_DIR) $(STAGING_DIR) $(TOOLCHAIN_DIR) $(BUILD_DIR_TOOLCHAIN); \
+		mkdir -p $(TOOLCHAIN_DIR)/stamp; \
+		mv $(TMP_DIR)/.ver_check $@; \
+	}
 
-$(STAGING_DIR)/.prepared: $(STAGING_DIR)/.toolchain_ver_check
-$(TOOLCHAIN_DIR)/stamp/.gcc-initial_installed: $(STAGING_DIR)/.prepared
+$(TOOLCHAIN_DIR)/info.mk $(STAGING_DIR)/.prepared: $(TOOLCHAIN_DIR)/stamp/.ver_check
 endif
 
 # prerequisites for the individual targets