[libj6] Move _init_libc to _init_libj6

As part of the move of jsix-specific code from libc to libj6, all the
library initialization is now libj6-specific, so move it all over.

src/libraries/j6/init.cpp

@@ -0,0 +1,41 @@
+#include <stdint.h>
+#include <j6/init.h>
+#include <j6/types.h>
+
+static size_t __initc = 0;
+static struct j6_init_value *__initv = 0;
+
+j6_handle_t __handle_sys = j6_handle_invalid;
+j6_handle_t __handle_self = j6_handle_invalid;
+
+extern "C" void
+_get_init(size_t *initc, struct j6_init_value **initv)
+{
+	if (!initc)
+		return;
+
+	*initc = __initc;
+	if (initv)
+		*initv = __initv;
+}
+
+extern "C" void
+_init_libj6(uint64_t *rsp)
+{
+	uint64_t argc = *rsp++;
+	rsp += argc;
+
+	__initc = *rsp++;
+	__initv = (struct j6_init_value *)rsp;
+
+	for (unsigned i = 0; i < __initc; ++i) {
+		if (__initv[i].type == j6_init_handle_other &&
+			__initv[i].handle.type == j6_object_type_system) {
+			__handle_sys = __initv[i].handle.handle;
+		}
+		else if (__initv[i].type == j6_init_handle_self &&
+			__initv[i].handle.type == j6_object_type_process) {
+			__handle_self = __initv[i].handle.handle;
+		}
+	}
+}