Only return JVMTI env if native agents are enabled

Author: gilles-duboscq

espresso/src/com.oracle.truffle.espresso/src/com/oracle/truffle/espresso/EspressoOptions.java

@@ -640,7 +640,7 @@ public Long apply(String size) {
                     usageSyntax = "false|true") //
     public static final OptionKey<Boolean> EnableSignals = new OptionKey<>(false);
 
-    @Option(help = "Enables java agents. Support is currently very limited.", //
+    @Option(help = "Enables native JVMTI agents. Support is currently very limited.", //
                     category = OptionCategory.EXPERT, //
                     stability = OptionStability.EXPERIMENTAL, //
                     usageSyntax = "false|true") //

espresso/src/com.oracle.truffle.espresso/src/com/oracle/truffle/espresso/vm/VM.java

@@ -1593,7 +1593,7 @@ public int GetEnv(@Pointer TruffleObject vmPtr_, @Pointer TruffleObject envPtr,
             return JNI_ERR;
         }
         TruffleObject interopPtr = null;
-        if (JVMTI.isJvmtiVersion(version)) {
+        if (getContext().getEspressoEnv().EnableNativeAgents && JVMTI.isJvmtiVersion(version)) {
             // JVMTI is requested before the main thread is created.
             // Also note that every request of a JVMTI env returns a freshly created structure.
             interopPtr = jvmti.create(version);