http://sourceware.org/ml/gdb-patches/2013-07/msg00236.html
gdb/ChangeLog
* mi/mi-main.c (output_register): Make MI 'r' format use standard
'z' format code. Remove error for optimized out values, standard
code will handle these fine.
gdb/testsuite/ChangeLog
* gdb.mi/mi-reg-undefined.exp: New file.
* gdb.mi/mi-reg-undefined.c: Likewise.
* gdb.mi/mi-reg-undefined.S: Likewise.