Use TREBLE_TESTING_OVERRIDE only in FMQ unit test client.

Usage of the env variable in the FMQ unit test service
was causing oneway methods to execute in a separate
thread which was causing timing issues and resultant
flakiness for some test cases.

Bug: 63825555
Test: Ran fmq_test 1000 times on Marlin
Change-Id: I9f752181e6fba0ef8f82216e513261c0861ef90e
diff --git a/tests/fmq_test b/tests/fmq_test
index 02683c9..7c5bfbe 100644
--- a/tests/fmq_test
+++ b/tests/fmq_test
@@ -1,6 +1,6 @@
 source /data/nativetest64/hidl_test_helper
 
-TREBLE_TESTING_OVERRIDE=true run_all_tests \
+run_all_tests \
     "/data/nativetest/android.hardware.tests.msgq@1.0-service-test/android.hardware.tests.msgq@1.0-service-test" \
     "/data/nativetest64/android.hardware.tests.msgq@1.0-service-test/android.hardware.tests.msgq@1.0-service-test" \
     "/data/nativetest/mq_test_client/mq_test_client" \
diff --git a/tests/msgq_test_client.cpp b/tests/msgq_test_client.cpp
index 4416c54..6cefb63 100644
--- a/tests/msgq_test_client.cpp
+++ b/tests/msgq_test_client.cpp
@@ -890,3 +890,9 @@
         ASSERT_FALSE(mQueue->read(&readData[0], mNumMessagesMax));
     }
 }
+
+int main(int argc, char** argv) {
+    setenv("TREBLE_TESTING_OVERRIDE", "true", true);
+    ::testing::InitGoogleTest(&argc, argv);
+    return RUN_ALL_TESTS();
+}