Fix testsuite/g++.old-deja/g++.mike/p658.C build failure on VxWorks RTP

[Mike Stump]

On Dec 22, 2020, at 1:45 PM, Alexandre Oliva <oliva@adacore.com> wrote:
> 
> The conflicting definition of OK is present in VxWorks RTP headers too.
> 
> Regstrapped on x86_64-linux-gnu, and tested with -x-arm-wrs-vxworks7r2.
> Ok to install?

Ok.

Ok to stylize all the #undef in the same way.  This is one happens to use a slightly different stye then the others as I recall.