clang provides libunwind.h and cmake adds a check to
find libunwind when this header is detected, which was
not the case with automake. The check however is expecting
specific unwinder implementation which provides libunwind-generic
solib, this is not a standard library that all implementations
will provide, therefore make this check optional.
Signed-off-by: Khem Raj <raj.khem@gmail.com> Cc: Andreas Müller <schnitzeltony@gmail.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
