audio/xmms-sapp, audio/penguinsap: Rework exception flags

The wrong C++ flag, --no-exceptions, was being passed to these ports. The
correct flag is "-fno-exceptions". Apparently gcc accepts the former, but
clang does not.

The current code states that clang version 3.2 will accept --no-exceptions,
but this isn't the case either. However, both of these ports will build
without a no-exceptions flag with clang. GCC still requires it.

Rework the clang detection code. If code is not detected, -fno-exceptions
is added to CXXFLAGS, otherwise nothing is done. Besides fixing the flag
handling, this implemention avoids the bmake errors that _CLANG!= was
generating.

Approved by: bapt (mentor), maintainer