Fix lack of FlexLexer include dir.

.github/bin/make-compilation-db.sh

@@ -18,9 +18,19 @@ set -e
 
 BANT=${BANT:-bant}
 
+if [ ! -e bazel-bin ]; then
+  echo "Before creating compilation DB, need to run bazel build first"
+  exit 1
+fi
+
 if command -v ${BANT} >/dev/null; then
   ${BANT} compile-flags > compile_flags.txt
+
+  # Bant does not see yet the flex dependency inside the toolchain
+  for d in bazel-out/../../../external/*flex*/src/FlexLexer.h ; do
+    echo "-I$(dirname $d)" >> compile_flags.txt
+  done
 else
-  echo "To create compilation DB, need to have http://bant.build/ installed."
+  echo "To create compilation DB, need to have http://bant.build/ installed or provided in BANT environment variable."
   exit 1
 fi