Move threading calls into a basic user space library.

lib/mammoth/src/debug.cpp

@@ -0,0 +1,5 @@
+#include "include/mammoth/debug.h"
+
+#include "zcall.h"
+
+void dbgln(const char* str) { ZDebug(str); }

lib/mammoth/src/thread.cpp

@@ -0,0 +1,19 @@
+#include "include/mammoth/thread.h"
+
+#include "zcall.h"
+
+namespace {
+
+extern "C" void thread_entry(Thread::Entry entry, void* arg1) {
+  entry(arg1);
+
+  ZThreadExit();
+}
+
+}  // namespace
+
+Thread::Thread(Entry e, const void* arg1) {
+  ZThreadCreate(Z_INIT_PROC_SELF, &thread_cap_);
+  ZThreadStart(thread_cap_, reinterpret_cast<uint64_t>(thread_entry),
+               reinterpret_cast<uint64_t>(e), reinterpret_cast<uint64_t>(arg1));
+}