[vm/fuzzer] add --enable-asserts to AOT step

Rationale:
This exposes certain bugs in a cleaner way
than just crashing. See bug for an example.

dart-lang#38965
dart-lang#38979

Change-Id: Ib6ce52e31d5ca539fb4aedab989638949751627f
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/122168
Reviewed-by: Alexander Markov <alexmarkov@google.com>
Commit-Queue: Aart Bik <ajcbik@google.com>

runtime/tools/dartfuzz/dartfuzz_test.dart

@@ -187,6 +187,7 @@ class TestRunnerAOT implements TestRunner {
     snapshot = '$tmp/snapshot';
     env = Map<String, String>.from(e);
     env['DART_CONFIGURATION'] = tag;
+    env['DART_VM_FLAGS'] = '--enable-asserts';
     cmd = [precompiler, ...extraFlags, fileName, snapshot];
   }
 
@@ -200,8 +201,11 @@ class TestRunnerAOT implements TestRunner {
   }
 
   void printReproductionCommand() {
-    print(
-        ["DART_CONFIGURATION=${env['DART_CONFIGURATION']}", ...cmd].join(" "));
+    print([
+      "DART_CONFIGURATION='${env['DART_CONFIGURATION']}'",
+      "DART_VM_FLAGS='${env['DART_VM_FLAGS']}'",
+      ...cmd
+    ].join(" "));
     print([dart, snapshot].join(" "));
   }