Okay, I've suddenly found the problem.
The compiler installation directory was set to "/home/developer/Development/svn/Tools/crosstools-ng/bin/bin".
This must be "/home/developer/Development/svn/Tools/crosstools-ng/bin" instead.
Strangely yesterday I've correctly set this directory, being the reason debugging worked.
Also strange is that code blocks still found the debugger, but just failed to form the correct commands. It wouldn't be bad if there was some error message if the toolchain executables are not in the bin sub directory of the path set in "Compiler's installation directory" ...
As I answered my own question, I hope this one helps others in the future.