[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.cpp

@@ -7,10 +7,27 @@
 namespace panic {
 
 void
-print_header(serial_port &out, const char *message)
+print_header(
+        serial_port &out,
+        const char *message,
+        const char *function,
+        const char *file,
+        uint64_t line)
 {
     out.write("\n\n\e[5;31m PANIC:\e[0;1;31m ");
-    out.write(message);
+    if (message) {
+        out.write(message);
+        out.write("\n ");
+    }
+    out.write(function);
+    out.write("  ");
+    out.write(file);
+    out.write(":");
+
+    char linestr[6];
+    snprintf(linestr, sizeof(linestr), "%d", line);
+    out.write(linestr);
+
     out.write("\n \e[0;31m===================================================================================\n");
 }