Thanks for both replies - I did follow the instructions on codesigning and everything appeared to work.
Complete error message is
--------------------------------------------
The GDB command:
"-gdb-set confirm off"
did not return any result.
The GDB process is no longer running.
--------------------------------------------
and the executable looks to be correctly signed:
Executable=/usr/local/Cellar/gdb/8.1/bin/gdb
Identifier=org.gnu.gdb
Format=Mach-O thin (x86_64)
CodeDirectory v=20100 size=62396 flags=0x0(none) hashes=1946+2 location=embedded
Hash type=sha256 size=32
CandidateCDHash sha256=37f81e9e2c57681b6ad94e4285efca2269b0aa0e
Hash choices=sha256
CDHash=37f81e9e2c57681b6ad94e4285efca2269b0aa0e
Signature size=1834
Authority=gdb-cert
Signed Time=5 Apr 2018, 07:34:59
Info.plist entries=4
TeamIdentifier=not set
Sealed Resources=none
Internal requirements count=1 size=88
and yes, the IDE works fine without debugging but that's of limited use
Thanks again for any advice.
John