findstring/MAKEFLAGS example is not robust

[Peter Eisentraut]

The manual contains this example:

     archive.a: ...
     ifneq (,$(findstring t,$(MAKEFLAGS)))
             +touch archive.a
             +ranlib -t archive.a
     else
             ranlib archive.a
     endif

But this would also trigger if you ran make with any other option that
contains a "t", for example --no-print-directory.

Is there a better way to write this?