Move RMA::Label out of the class, so it can be forward declared.

test/cctest/compiler/test-run-native-calls.cc

Index: test/cctest/compiler/test-run-native-calls.cc
diff --git a/test/cctest/compiler/test-run-native-calls.cc b/test/cctest/compiler/test-run-native-calls.cc
index 3c64bc1295bcb6460c7e5ca98268cbbaaaa287c2..9311c02748e08e8fa2f126dba957aca650861473 100644
--- a/test/cctest/compiler/test-run-native-calls.cc
+++ b/test/cctest/compiler/test-run-native-calls.cc
@@ -21,8 +21,6 @@ namespace v8 {
 namespace internal {
 namespace compiler {
 
-typedef RawMachineAssembler::Label MLabel;
-
 #if V8_TARGET_ARCH_ARM64
 // TODO(titzer): fix native stack parameters on arm64
 #define DISABLE_NATIVE_STACK_PARAMS true