Put GC implementations into separate modules.

The mm module now compiles separately for each GC implementation.

kotlin-native/backend.native/cli.bc/src/org/jetbrains/kotlin/cli/bc/K2Native.kt

@@ -206,7 +206,7 @@ class K2Native : CLICompiler<K2NativeCompilerArguments>() {
 
                 put(ENABLE_ASSERTIONS, arguments.enableAssertions)
 
-                put(MEMORY_MODEL, when (arguments.memoryModel) {
+                val memoryModel = when (arguments.memoryModel) {
                     "relaxed" -> {
                         configuration.report(STRONG_WARNING, "Relaxed memory model is not yet fully functional")
                         MemoryModel.RELAXED
@@ -217,7 +217,9 @@ class K2Native : CLICompiler<K2NativeCompilerArguments>() {
                         configuration.report(ERROR, "Unsupported memory model ${arguments.memoryModel}")
                         MemoryModel.STRICT
                     }
-                })
+                }
+
+                put(MEMORY_MODEL, memoryModel)
 
                 when {
                     arguments.generateWorkerTestRunner -> put(GENERATE_TEST_RUNNER, TestRunnerKind.WORKER)
@@ -271,6 +273,26 @@ class K2Native : CLICompiler<K2NativeCompilerArguments>() {
                         DestroyRuntimeMode.ON_SHUTDOWN
                     }
                 })
+                val assertGcSupported = {
+                    if (memoryModel != MemoryModel.EXPERIMENTAL) {
+                        configuration.report(ERROR, "-Xgc is only supported for -memory-model experimental")
+                    }
+                }
+                put(GARBAGE_COLLECTOR, when (arguments.gc) {
+                    null -> GC.SINGLE_THREAD_MARK_SWEEP
+                    "noop" -> {
+                        assertGcSupported()
+                        GC.NOOP
+                    }
+                    "stms" -> {
+                        assertGcSupported()
+                        GC.SINGLE_THREAD_MARK_SWEEP
+                    }
+                    else -> {
+                        configuration.report(ERROR, "Unsupported GC ${arguments.gc}")
+                        GC.SINGLE_THREAD_MARK_SWEEP
+                    }
+                })
             }
         }
     }

kotlin-native/backend.native/cli.bc/src/org/jetbrains/kotlin/cli/bc/K2NativeCompilerArguments.kt

@@ -305,6 +305,9 @@ class K2NativeCompilerArguments : CommonCompilerArguments() {
     @Argument(value="-Xdestroy-runtime-mode", valueDescription = "<mode>", description = "When to destroy runtime. 'legacy' and 'on-shutdown' are currently supported. NOTE: 'legacy' mode is deprecated and will be removed.")
     var destroyRuntimeMode: String? = "on-shutdown"
 
+    @Argument(value="-Xgc", valueDescription = "<gc>", description = "GC to use, 'noop' and 'stms' are currently supported. Works only with -memory-model experimental")
+    var gc: String? = null
+
     override fun configureAnalysisFlags(collector: MessageCollector): MutableMap<AnalysisFlag<*>, Any> =
             super.configureAnalysisFlags(collector).also {
                 val useExperimental = it[AnalysisFlags.useExperimental] as List<*>