Fix tidy warning

Prefer FIXME to TODO

src/librustc_back/target/fuchsia_base.rs

@@ -25,7 +25,7 @@ pub fn opts() -> TargetOptions {
             // resolutions the linker does). This option only applies to all
             // following libraries so we're sure to pass it as one of the first
             // arguments.
-            // TODO: doesn't seem to be supported by clang toolchain
+            // FIXME: figure out whether these linker args are desirable
             //"-Wl,--as-needed".to_string(),
 
             // Always enable NX protection when it is available

src/libstd/sys/unix/thread.rs

@@ -137,7 +137,7 @@ impl Thread {
     }
     #[cfg(target_os = "fuchsia")]
     pub fn set_name(_name: &CStr) {
-        // TODO: determine whether Fuchsia has a way to set a thread name.
+        // FIXME: determine whether Fuchsia has a way to set a thread name.
     }
 
     pub fn sleep(dur: Duration) {