don't use NoMem as input for const calls with compound parameters

Compound types are not modeled as direct SSA values in firm, so we need
to use memory operations and therefore need a real memory input even for
const functions in this case.

This should fix opt/fehler221.c
rename --external-cpp to -no-integrated-cpp (like gcc)
warn about '/*' in comments
use integrated preprocessor by default unless crosscompiling