This patch introduces a function in gdbserver-support.exp to find out
whether the current target is GDBserver.
The code was inspired from gdb.trace/qtro.exp, so it replaces the code
there by a call to the new function.
gdb/testsuite/ChangeLog:
* gdb.trace/qtro.exp: Replace gdbserver detection code by...
* lib/gdb.exp (target_is_gdbserver): New
procedure.