cmake: Find TBB dependency in Config.cmake.in when building static (#3557)
cmake: Find TBB dependency in Config.cmake.in when building static (#3557)

TBB::tbb is added as a library dependency via TARGET_NAME_IF_EXISTS.
Therefore if an executable links OpenImageIO static library without the
executable itself depending on TBB, then TBB will not be linked in and
result in link time errors.
lgritz/oiio,lgritz/oiio,lgritz/oiio,OpenImageIO/oiio,lgritz/oiio,OpenImageIO/oiio,OpenImageIO/oiio,OpenImageIO/oiio