Build using Toothpick scripts (#122)

Co-authored-by: BillyGalbreath <blake.galbreath@gmail.com>

buildSrc/src/main/kotlin/task/InitGitSubmodules.kt

@@ -0,0 +1,21 @@
+package task
+
+import gitCmd
+import org.gradle.api.Project
+import org.gradle.api.Task
+import taskGroup
+import upstreamDir
+
+internal fun Project.createInitGitSubmodulesTask(
+    receiver: Task.() -> Unit = {}
+): Task = tasks.create("initGitSubmodules") {
+    receiver(this)
+    group = taskGroup
+    onlyIf { !upstreamDir.resolve(".git").exists() }
+    doLast {
+        val exit = gitCmd("submodule", "update", "--init", "--recursive", printOut = true).exitCode
+        if (exit != 0) {
+            error("Failed to checkout git submodules: git exited with code $exit")
+        }
+    }
+}