Add HULK header; map virtual memory for HULK bss section

src/hulk/header.d

@@ -0,0 +1,23 @@
+/**
+ * HULK image header.
+ */
+module hulk.header;
+
+/**
+ * Header describing the HULK image.
+ */
+struct Header
+{
+    /**
+     * Total size of memory to be mapped.
+     *
+     * The OS loader must ensure that virtual memory is mapped for this entire
+     * size.
+     * This value is really an integer, but is stored as a pointer because it
+     * is provided by the linker and LDC does not like us to cast it.
+     */
+    void * total_size;
+
+    /** Entry point. */
+    void * entry;
+}