uclibc++: remove

uclibc++: remove

No package here depends on it. Furthermore, uClibc++ is a fairly buggy
C++ library and seems to be relatively inactive upstream.

It also lacks proper support for modern C++11 features.

The main benefit of it is size: 66.6 KB	vs 287.3 KB on mips24kc. Static
linking and LTO can help bring the size down of packages that need it.

Added warning message to uclibc++.mk

Signed-off-by: Rosen Penev <rosenp@gmail.com>
Acked-by: Hauke Mehrtens <hauke@hauke-m.de>