scripts/detect_cc.sh: make C vs C++ warning non-fatal
Even if we detect that $CC and $CXX are different types, we should
continue so that mk/cc.mk is still generated.
Change-Id: I551e2d9149ea982d3c9973dfc5f2557f12fbc337
Signed-off-by: Daniel Verkamp <daniel.verkamp@intel.com>