Is there any possibility that output from GDB could, at any point _other_ than its initial output line return the characters "GNU gdb" at the beginning of any output line? (Could it happen as the result of a user doing a command via the debug console that resulted in text display that might contain any arbitrary data, including that key string? Is there any such command? List of a source file that might hold that at the beginning of one of the lines?)
If so, then it appears that the (c::b) internally maintained version information for GDB could become corrupted.
(The concern would also apply to any of the other strings that are checked for [like the ones leading to "quit"ting the debugger], where they might result in undesireable behaviour if possible for them to occur in other than the appropriate situations.)