plugins: pow - remove unneeded vars

Signed-off-by: Tim Blechmann <tim@klingt.org>
supernova: remove dead code

Signed-off-by: Tim Blechmann <tim@klingt.org>
supernova: we require c++11 now

Signed-off-by: Tim Blechmann <tim@klingt.org>
sclang: make c++11-ready on osx

Signed-off-by: Tim Blechmann <tim@klingt.org>
cmake: better clang detection

Signed-off-by: Tim Blechmann <tim@klingt.org>
testsuite: on apple/clang we want to link with libc++

Signed-off-by: Tim Blechmann <tim@klingt.org>