Enable function sections on windows-gnu

Author: mati865

src/librustc_target/spec/windows_gnu_base.rs

@@ -66,8 +66,6 @@ pub fn opts() -> TargetOptions {
     );
 
     TargetOptions {
-        // FIXME(#13846) this should be enabled for windows
-        function_sections: false,
         linker: Some("gcc".to_string()),
         dynamic_linking: true,
         executables: true,