Two changes in this patch are related to c6x, while the other two are
not related to c6x very much, which are about uclinx on NON-MMU machine.

Both gdb.base/savedregs.exp and gdb.mi/mi-syn-frame.exp expects to get
an exception when access memory of address 0x0.  It doesn't work on
NON-MMU machine.

Actually, this has been discussed in this thread,

  http://sourceware.org/ml/gdb-patches/2011-06/msg00124.html
  [patch, testsuite] gdb.base/savedregs.exp: SIGSEGV -> SIGILL

The final conclusion is that we use SIGILL for NON-MMU machine, and
continue to use SIGSEGV for MMU machine.  Changes in this patch is
implemented in this way.

-- 
Yao (齐尧)