I build a kernel with said flag settings but unfortunately it panicked
at bootup (though after detecting the drives and even the bwtwo
lateron) 

I don't at all know if it's related to the esp flags (it may have been
at the point where the internal drive gets accessed for reading rc)

Unfortunately (unrelated to the esp thing) I have not been able to
build a debugging kernel, even when my regular compile finishes
perfectly fine. (The debugging kernel I simply created by copying my
description file and  removing the # in front of
"options        DEBUG           # kernel debugging code"

The result is that I get nm complaining about __main.o in
lib/libkern. Like I mentioned, there is no problem whatsoever in my
regular compile.

Any suggestions?

Joe.