libbinder: fix flake-mode build

Compile option to introduce random sleeps in the code to make
certain rare flakes easier to reproduce.

Bug: 244325464
Test: binderRpcTest w/ flake mode on
Change-Id: Ibb78987f6550e0d6ec39b527059bfc517ea04492
diff --git a/libs/binder/RpcState.cpp b/libs/binder/RpcState.cpp
index c0e36c4..c411f4f 100644
--- a/libs/binder/RpcState.cpp
+++ b/libs/binder/RpcState.cpp
@@ -41,7 +41,7 @@
 #if RPC_FLAKE_PRONE
 void rpcMaybeWaitToFlake() {
     [[clang::no_destroy]] static std::random_device r;
-    [[clang::no_destroy]] static std::mutex m;
+    [[clang::no_destroy]] static RpcMutex m;
     unsigned num;
     {
         RpcMutexLockGuard lock(m);