In CMake 2.4 the generated link line for a target always preserved the
originally specified libraries in their original order.  Dependencies
were satisfied by inserting extra libraries into the line, though it had
some bugs.  In CMake 2.6.0 we preserved only the items on the link line
that are not known to be shared libraries.  This reduced excess
libraries on the link line.  However, since we link to system libraries
(such as /usr/lib/libm.so) by asking the linker to search (-lm), some
linkers secretly replace the library with a static library in another
implicit search directory (developers can override this by using an
imported target to force linking by full path).  When this happens the
order still matters.

To avoid this and other potential subtle issues this commit restores
preservation of all non-target items and static library targets.  This
will create cases of unnecessary, duplicate shared libraries on the link
line if the user specifies them, but at least it will work.  In the
future we can attempt a more advanced analysis to safely remove
duplicate shared libraries from the link line.