[sanitize] Don't build older then 1h requests

Temp workaround for llvm#250.

Author: vitalybuka

zorg/buildbot/builders/sanitizers/buildbot_functions.sh

@@ -144,6 +144,11 @@ function buildbot_update {
       git checkout -f "${BUILDBOT_REVISION}"
       git status
       git rev-list --pretty --max-count=1 HEAD
+      # FIXME: Workaround for https://github.com/llvm/llvm-zorg/issues/250
+      [[ "${SKIP_OLD:-1}" == "0" ]] || (git log -1 --after='3 hours ago' | grep .) || {
+        echo Revision is not recent enough
+        exit 1
+      }
     ) || { build_exception ; exit 1 ; }
     LLVM=$ROOT/llvm-project/llvm
   fi
@@ -204,7 +209,7 @@ function build_clang_at_release_tag {
   then
     echo "@@@BUILD_STEP using pre-built stage1 clang at r${host_clang_revision}@@@"
   else
-    BUILDBOT_MONO_REPO_PATH= BUILDBOT_REVISION="${host_clang_revision}" buildbot_update
+    SKIP_OLD=0 BUILDBOT_MONO_REPO_PATH= BUILDBOT_REVISION="${host_clang_revision}" buildbot_update
 
     rm -rf ${STAGE1_DIR}
     echo @@@BUILD_STEP build stage1 clang at $host_clang_revision@@@