binder: declare main in global NS, w/o extern "C"

The main function should be in the global namespace, not the android
namespace. We were using 'extern "C"' to prevent the mangling, but the
C++ standard doesn't allow a linkage-specification for main,
https://eel.is/c++draft/basic.start.main#3.sentence-5:

"The main function shall not be declared with a linkage-specification
([dcl.link])."

Clang has started warning on incorrect declarations of main (-Wmain).

Bug: http://b/379133546
Test: m binder_thread_stats libbinderdebug_test binderSafeInterfaceTest
Change-Id: I1c53ce621391b5577c8c04b21117e9b59fe05136

Author: rprichard

libs/binder/tests/binderSafeInterfaceTest.cpp

@@ -858,7 +858,13 @@ TEST_F(SafeInterfaceTest, TestIncrementTwo) {
     ASSERT_EQ(b + 1, bPlusOne);
 }
 
-extern "C" int main(int argc, char **argv) {
+} // namespace tests
+} // namespace android
+
+int main(int argc, char** argv) {
+    using namespace android;
+    using namespace android::tests;
+
     testing::InitGoogleTest(&argc, argv);
 
     if (fork() == 0) {
@@ -875,6 +881,3 @@ extern "C" int main(int argc, char **argv) {
 
     return RUN_ALL_TESTS();
 }
-
-} // namespace tests
-} // namespace android

libs/binderdebug/stats.cpp

@@ -22,9 +22,9 @@
 
 #include <inttypes.h>
 
-namespace android {
+int main() {
+    using namespace android;
 
-extern "C" int main() {
     // ignore args - we only print csv
 
     // we should use a csv library here for escaping, because
@@ -58,5 +58,3 @@ extern "C" int main() {
     }
     return 0;
 }
-
-} // namespace android

libs/binderdebug/tests/binderdebug_test.cpp

@@ -60,8 +60,15 @@ TEST(BinderDebugTests, BinderThreads) {
     EXPECT_GE(pidInfo.threadCount, 1);
 }
 
-extern "C" {
+} // namespace  test
+} // namespace  binderdebug
+} // namespace  android
+
 int main(int argc, char** argv) {
+    using namespace android;
+    using namespace android::binderdebug;
+    using namespace android::binderdebug::test;
+
     ::testing::InitGoogleTest(&argc, argv);
 
     // Create a child/client process to call into the main process so we can ensure
@@ -84,7 +91,3 @@ int main(int argc, char** argv) {
 
     return RUN_ALL_TESTS();
 }
-} // extern "C"
-} // namespace  test
-} // namespace  binderdebug
-} // namespace  android