Fix configuration of a static MSVC build (#864)
Fix configuration of a static MSVC build (#864)

MSVC uses .lib files for its libraries so setting the suffix to .a prevents find_library from functioning.

Also don't use unix libraries with MSVC.
libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl