The error is within xCode.

As guessed,  the corresponding file CFLocale.h a.s.o.  are missing.

I own two iMacs. xCode on the older one is not corrupted. The Problem occurred with the newer one

2.8 GHz Intel Core i7, 4GB 1067 MHz DDR3

I bought it about a year ago and installed the developers tool from the distribution DVD. Before contacting the FB news group I checked and found out, that the xCode has been updated  regularly by the automatic updates sent by Apple. I counter checked the version on Apple's  developers site. Of Course I am not a beta tester, but good to know anyway.

(FB is the only programming software I use on the Mac (starting way back with FB 1 I guess in the early nineties) beside of Supercard, which is something different anyway. Oh, and I want to learn the "new" imagej macro language, too.)

Problem is solved for the moment:

I installed the xCode from the distribution DVD again. The deinstallation was to "dangerous" for me. But, thank to you, the run and compiling went through smoothly. 

Thank You ! The problem is solved, though I cannot explain why it happened at first instance. Hopefully, it is not going to happen again.

Have a nice day

Bernard R