build: Refactor to ensure all headers run through compile

Change-Id: I06089ea54ace1acd79d4d12d9b7eb6cc01b38596
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/src/cancel.cpp b/src/cancel.cpp
new file mode 100644
index 0000000..78f29c3
--- /dev/null
+++ b/src/cancel.cpp
@@ -0,0 +1 @@
+#include <stdplus/cancel.hpp>