The bug report has been closed already. Here the comment of the assignee:
1. QChar c; for(; c <= 'z'; ++c) does not compile.

2. What can be used in breakpoint conditioned is defined by what the underlying debugger (GDB here) is able to handle. It is not possible to have arbitrary C++ code there, specifically you cannot call functions that are not present in the binary, e.g. because they are inlined by the compiler or have not been used in the application code, so the linker had no reason to include it.

3. You can fiddle around with something along the lines of creating a breakpoint using gdb's python interface and a condition based on some translation of set $s = QString::toLatin1_helper(test) / set $p = $s.d.offset + (char)$s.d / strcmp($p, "d"), but that's not worth it as long as you can modify the code and put the condition in the code.*