support case insensitive windows .lib/.Lib suffix
I use clang-cl to cross build for windows on a case sensitive filesystem. Windows library names in windows sdk are not consistent, their suffix can be .lib or .Lib. I linking Ole32.Lib, I can not write target_link_libraries(... Ole32) because Ole32.lib does not exits. The only option I can find out is target_link_libraries(... Ole32.Lib), but cmake generates Ole32.Lib.lib. Recognizing .Lib as a full library name for windows will be better.