Move to Weld as the build system.

Change-Id: I7c9704f3f310cf7e5410db148a9c4c589914b0f2
diff --git a/mod/greeting/source/greeting.cpp b/mod/greeting/source/greeting.cpp
new file mode 100644
index 0000000..0fb811d
--- /dev/null
+++ b/mod/greeting/source/greeting.cpp
@@ -0,0 +1,17 @@
+#include <greeting/greeting.hpp>
+
+#include <sstream>
+
+namespace greeting {
+
+std::string make_greeting(std::string const& greetee) {
+  if (greetee == "") {
+    return "Hello!";
+  } else {
+    std::ostringstream out;
+    out << "Hello " << greetee << "!";
+    return out.str();
+  }
+}
+
+}