remove an invalid FIXME note

Signed-off-by: onur-ozkan <work@onurozkan.dev>

src/bootstrap/src/lib.rs

@@ -635,11 +635,12 @@ impl Build {
         if self.config.backtrace {
             features.insert("backtrace");
         }
+
         if self.config.profiler_enabled(target) {
             features.insert("profiler");
         }
-        // Generate memcpy, etc.  FIXME: Remove this once compiler-builtins
-        // automatically detects this target.
+
+        // If zkvm target, generate memcpy, etc.
         if target.contains("zkvm") {
             features.insert("compiler-builtins-mem");
         }