When TC_CXX_RUNTIME is set to be 'llvm' then clang looks for
libcxx to provide C++ runtime and unwinding library
(From OE-Core rev: aba2d949818b032222dbaed98e38cd29e3c992b6)
Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>