Do not pass -C passes=... when nightly is used and plugins are compiled

cargo-afl/src/main.rs

@@ -241,13 +241,12 @@ where
     let binding = common::afl_llvm_dir();
     let p = binding.display();
 
-    let mut rustflags = format!(
+    let mut rustflags = String::from(
         "-C debug-assertions \
              -C overflow_checks \
-             -C passes={passes} \
              -C codegen-units=1 \
              -C opt-level=3 \
-             -C target-cpu=native "
+             -C target-cpu=native ",
     );
     let mut environment_variables = HashMap::<&str, String>::new();
     environment_variables.insert("ASAN_OPTIONS", asan_options);
@@ -271,13 +270,14 @@ where
 
         environment_variables.insert("AFL_QUIET", "1".to_string());
     } else {
-        rustflags.push_str(
-            "-C llvm-args=-sanitizer-coverage-level=3 \
+        rustflags.push_str(&format!(
+            "-C passes={passes} \
+            -C llvm-args=-sanitizer-coverage-level=3 \
             -C llvm-args=-sanitizer-coverage-trace-pc-guard \
             -C llvm-args=-sanitizer-coverage-prune-blocks=0 \
             -C llvm-args=-sanitizer-coverage-trace-compares
             ",
-        );
+        ));
     }
 
     let no_cfg_fuzzing = env::var("AFL_NO_CFG_FUZZING").is_ok();