That macro currently was broken. It added flags to $CFLAGS but then called the
C++ compiler. The result was that ZNC didn't compile with GCC 3, because it
tried to use -fvisibility=hidden which isn't supported in that GCC version.
A list of changes done to this macro is contained in a comment.
Signed-off-by: Uli Schlachter <psychon@znc.in>