[source] toolchain: force a full rebuild on buildbot if the toolchain changed

[LEDE Commits]

nbd pushed a commit to source.git, branch master:
https://git.lede-project.org/bd3a5ca19006fdb144e34a96f6889f36aa147611

commit bd3a5ca19006fdb144e34a96f6889f36aa147611
Author: Felix Fietkau <nbd at nbd.name>
AuthorDate: Wed Feb 15 15:15:46 2017 +0100

    toolchain: force a full rebuild on buildbot if the toolchain changed
    
    Signed-off-by: Felix Fietkau <nbd at nbd.name>
---
 toolchain/Makefile | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/toolchain/Makefile b/toolchain/Makefile
index 6ee8811..34abda2 100644
--- a/toolchain/Makefile
+++ b/toolchain/Makefile
@@ -69,6 +69,18 @@ ifneq ($(ARCH),)
 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 $@
+
+$(STAGING_DIR)/.prepared: $(STAGING_DIR)/.toolchain_ver_check
+$(TOOLCHAIN_DIR)/stamp/.gcc-initial_installed: $(STAGING_DIR)/.prepared
+endif
+
 # prerequisites for the individual targets
 $(curdir)/ := .config prereq
 $(curdir)//compile = $(STAGING_DIR)/.prepared $(TOOLCHAIN_DIR)/info.mk $(tools/stamp-compile)