[gdb/testsuite] Add selftest disassemble-s390x
In commit a98a6fa2d8e ("s390: Add arch15 instructions"), support for
new instructions was added to libopcodes, but the added tests only exercise
this for gas.
Add a unit test disassemble-s390x that checks gdb's ability to
disassemble one of these instructions:
...
$ gdb -q -batch -ex "maint selftest -v disassemble-s390x"
Running selftest disassemble-s390x.
0xb9 0x68 0x00 0x03 -> clzg %r0,%r3
Ran 1 unit tests, 0 failed
...
Tested on x86_64-linux and s390x-linux.
3 files changed
