Allow custom lib suffix be used as find path [v2]
Inspired by commit 896ad251 for bug #11260 (closed), this commit allows to use the variable CMAKE_FIND_LIBRARY_CUSTOM_LIB_SUFFIX to be used as find path. Allowing the find path to be more deterministic on custom setups.
A similar idea has already been suggested in #10287 (closed) and is required for bug #15994 (closed).
v2: - Change path variable a string to be specified as suffix directly. - Make path variable non-global - Fix find_library test - Strip FindPackage, as testing is ambigous in such scenario
The first version of the patch and the respective discussion can be found on the ML: