zlib's uri is a bit unstable as when they release a new version they
move the last release "elsewhere"
This change switches the upstream URI over to github, which should be
a bit more reliable.
webp 1.3 changed the filenames on windows to include a `lib` prefix
(ie libwebp.lib rather than webp.lib) now this is a common thing
on linux and cmake has a `CMAKE_FIND_LIBRARY_PREFIXES` variable that
has a list of prefixes to look for during a `find_library` call.
`CMAKE_FIND_LIBRARY_PREFIXES` gets set during the call to the
`project` method in the main CMakeLists of a project. Now for windows
`lib` is *not* a common prefix by CMake, and it doesn't add "lib" to
CMAKE_FIND_LIBRARY_PREFIXES during that call.
so find library doesn't look for it, the libs are not found and an
unhappy time is had by all. Now the most obvious solution would be to
pass `-DCMAKE_FIND_LIBRARY_PREFIXES=lib` to CMake to sidestep this
however, the `project` call will set the variable overwriting
anything you passed through the CLI.
So the fix here is to have `find_library` counter-intuitively look
for both `libwebp` and `webp`
The last webp update changed the filenames of the webp libraries
on windows causing oiio not to find them and oiio silently build
without webp support, which only came to light after all of
blender was build and a test failed.
This change makes the OIIO validate and error out if certain
dependencies are not found at configure time so these mistakes
are caught early.
Brecht Van Lommel
Ray molenkamp