We need to avoid declaring dependencies on strings which are valid
LINK_LIBS and not valid targets. Previously, we used if(TARGET) to
check this condition. However, if(TARGET) checks whether a target has
been created (in the cmake subdirectory traversal order) and not
whether it *will* be created. This results in annoying directory
This patch changes the check to more explicitly eliminate problematic
libraries (namely -lpthread) using a REGEX.