build: better error reporting in bootstrap

bootstrap

@@ -1,5 +1,18 @@
 #!/bin/sh
 
+# Check that the repository is properly set up
+if [ ! -x "./lol/bootstrap" ]; then
+cat << EOF
+Error: cannot execute lol/bootstrap
+
+Did you configure the Lol Engine submodule? The following may help:
+
+    git submodule update --init --recursive
+
+EOF
+    exit 1
+fi
+
 # Bootstrap this project first, using the Lol Engine script
 ./lol/bootstrap
 

lol

@@ -1 +1 @@
-Subproject commit e2770595450f709f2b841299ef6a1b7d5fa79a76
+Subproject commit 99c8c2353e082b20cf8d6f2a5501331dfc2a54ca