Distinguishing "true" MIPS box from DECstation at compile time

[Brain in Neutral]

How does one tell, when compiling a C program, whether the host is a
true MIPS machine (e.g., M/120) from a DECstation that's running
Ultrix.  I think I remember reading an article a while back that
complained about "mips" being defined by the preprocessor even on
Ultrix machines.  Is this true?  If so, is the test

# if mips
# if ultrix
	DECstation
# else
	true MIPS
# endif
# endif

Is there a nicer way?

Yours,
Paul DuBois
dubois at primate.wisc.edu