Although BUILD_CXXFLAGS, by default, expands to the same thing as
BUILD_CFLAGS there is no guarantee that this will be true in all
cases. When setting CXXFLAGS we should use the former.
(From OE-Core rev: fd75637d97cc3d669229e59c1d21ce7038fc92d7)
Signed-off-by: Phil Blundell <pb@pbcl.net>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>