[panic.serial] Add location to panic data

Updated kassert to be an actual function, and used the __builtin_*
functions for location data. Updated the panic handler protocol to
include sending location data as three more parameters. Updated the
serial panic handler to display that data along with the (optional)
message.

src/kernel/panic.serial/display.h

@@ -17,7 +17,13 @@ struct frame
     uintptr_t return_addr;
 };
 
-void print_header(serial_port &out, const char *message);
+void print_header(
+        serial_port &out,
+        const char *message,
+        const char *function,
+        const char *file,
+        uint64_t line);
+
 void print_callstack(serial_port &out, symbol_table &syms, frame const *fp);
 void print_cpu_state(serial_port &out, const cpu_state &regs);