eglibc-use-option-groups: Conditionally exclude c++ tests

eglibc-use-option-groups: Conditionally exclude c++ tests

Some test programs written in c++ are still included in spite of
"libc-cxx-tests" being omitted from DISTRO_FEATURES_LIBC.
All .cc programs are compiled with g++.
g++ automatically specifies linking against the C++ library.
This patch conditionally excludes the following tests as well:

  bug-atexit3-lib.cc
  tst-cancel24.cc
  tst-cancel24-static.cc
  tst-unique3lib.cc
  tst-unique3lib2.cc
  tst-unique4lib.cc
  tst-unique3.cc
  tst-unique4.cc

Tested with DISTRO_FEATURES_LIBC_remove = " libc-cxx-tests"

[YOCTO #7003]

Signed-off-by: Juro Bystricky <juro.bystricky@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>