gdb script: How can a script determine if it is invoked under `gdb` or `gdb-multiarch`?

Question

I'd like to define a command which does X under gdb-multiarch, but prints out a helpful message when run under normal gdb. How can my script determine which of the two its run under?

Why? When I start gdb-multiarch, I can bind to a qemu-arm session. When I try that in gdb, I get bizarre errors. It's easy to forget and run gdb (and not -multiarch), and I want to my bind-to-qemu tell me "This must be run under gdb-multiarch".