How to shut off X3.64 SGR in gdb output?

[Mouse <mouse%Rodents-Montreal.ORG@localhost>]

I've installed 9.1 (for work) and now find myself unable to get gdb to
stop trying to use X3.64 SGR control sequences, even though it not only
has no reason to think they'll work but has reason to think they won't.

Specifically, I'm using TERM=mterm (hence the "no reason to think
they'll work" and "reason to think they won't" - its description
includes nothing indicating anything even vaguely X3.64).  When I first
started using 9.1's gdb, I got horrors like

Program terminated with signal SIGABRT, Aborted.
#0  [34m0x00007e9f36d6791a[m in [33m_lwp_kill[m () from /usr/lib/libc.so.12
(gdb) 

where the [...m stuff is characteristic of something assuming SGR
sequences will work.  Looking at the gdb documentation, the only
mention of colours (or colors - I looked for both) I could find was in
the "style" section.  It said, in particular,

'set style enabled 'on|off''
     Enable or disable all styling.  The default is host-dependent, with
     most hosts defaulting to 'on'.

so I put "set style enabled off" in ~/.gdbinit.  This shut off the
worst of it, but I'm still seeing

[35;1mGNU gdb (GDB) 8.3
[mCopyright (C) 2019 Free Software Foundation, Inc.

on startup.

How do I get it to stop doing that?

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