Misuse of cmake link_directories to pass library filenames

[dmacks]

Lots of CMakeLists.txt have things such as:

link_directories(${FOO_LIBRARIES})

either alone or accompanied by:

target_link_libraries(bar ${FOO_LIBRARIES})

or

target_link_libraries(bar foo)

The variable ${FOO_LIBRARIES} contains the actual filename, not the path, so it should be passed directly via target_link_libraries(). Paths passed via link_directories() are supposed to be directories, and so they get passed as -L flags, which is not correct when passing the actual filename. And if there is a ${FOO_LIBRARIES}, that is what should be used rather than assuming that "foo" is the correct library name (overriding a user-specified alternative).

The typical symptom is a compile-time message such as:

ld: warning: -L path '/sw/lib/libusb.dylib' is not a directory

5d76e00 fixes a few of these cases, but there are still more.