Debugger: Remove workaround for gdb-7.1 bug

See sourceware.org/bugzilla/show_bug.cgi?id=12023.
The workaround can cause hickups in the output parser
of Mac gdb, as the error message is scattered within
regular output without any markup.

Change-Id: I835133e390403a0f8f6aa573d6f9c63cf0784187
Reviewed-by: hjk <hjk121@nokiamail.com>
Debugger: Hard-code version dependency of m_dissembleUsesComma

We don't support GDB in the range 7.0...7.3 anymore where the
outcome was unsure.

Change-Id: I1ce76f5c4b1febe45c4a3b6404208fed7d9c6868
Reviewed-by: hjk <hjk121@nokiamail.com>
Debugger: Disable some commands on Mac

Version of gdb < 7.4 means we are on Mac, so we can
disable commands that have known results there.

Change-Id: I8fc97ed61c47af2c3d9e5cc2bf83e97661204d4f
Reviewed-by: hjk <hjk121@nokiamail.com>