Ignore signedness check for uuid_t on DragonFly

Author: mneumann

libc-test/build.rs

@@ -264,12 +264,13 @@ fn main() {
         }
     });
 
-    cfg.skip_signededness(|c| {
+    cfg.skip_signededness(move |c| {
         match c {
             "LARGE_INTEGER" |
             "mach_timebase_info_data_t" |
             "float" |
             "double" => true,
+            "uuid_t" if dragonfly => true,
             n if n.starts_with("pthread") => true,
 
             // windows-isms