print/cups and -Wno-tautological-compare

[Edgar Fuß <ef%math.uni-bonn.de@localhost>]

I'm trying to build print/cups on OSX with clang.
Compiling C++ parts fails with
        cc1plus: error: unrecognized command line option 
"-Wno-tautological-compare"

The problem is that CC is clang, which does support that option, while CXX is 
g++, which does not.
CUPS' configure script detects that ,,GCC'' (i.e., clang) supports it and add 
it to the OPTIM variable, which later ends up in both CFLAGS and CXXFLAGS.

Can anyone think of a sane way of fixing that? Splitting OPTIM into OPTIM_C and 
OPTIM_CXX? Adding OPTIM_C and OPTIM_CXX while keeping OPTIM?