rust: fix darwin build

rust/hg-core/src/revlog/options.rs

@@ -113,7 +113,7 const fn can_populate_mmap() -> bool {
 
 /// There is a of populating mmaps for Windows, but it would need testing.
 #[cfg(not(target_os = "linux"))]
-const fn can_populate_mmap() {
+const fn can_populate_mmap() -> bool {
     false
 }
 

rust/hg-core/src/vfs.rs

@@ -37,7 +37,8 fn get_umask() -> u32 {
         // setting it? Doesn't this affect all threads in this tiny window?
         let mask = libc::umask(0);
         libc::umask(mask);
-        mask & 0o777
+        #[allow(clippy::useless_conversion)]
+        (mask & 0o777).into()
     })
 }