[runtimes][NFC] Consistently declare main() functions in tests (#162548)

In the libc++ test suite, we consistently declare main() functions with
full parameters and explicitly return from the function. This helps code
that compiles the tests with -ffreestanding, where main() is not a
special function (with an implicit return and special mangling).

This patch fixes a few stray declarations, including in libunwind and
libc++abi.

NOKEYCHECK=True
GitOrigin-RevId: 4f80c064eb2933c00c0ba9b7826aa3631cf3b5c2

test/forced_unwind4.pass.cpp

diff --git a/test/forced_unwind4.pass.cpp b/test/forced_unwind4.pass.cpp
index 15efca8..fbc8128 100644
--- a/test/forced_unwind4.pass.cpp
+++ b/test/forced_unwind4.pass.cpp
@@ -17,9 +17,7 @@
 
 // Android/Bionic does not support pthread_cancel.
 #ifdef __BIONIC__
-int main() {
-  return 0;
-}
+int main(int, char**) { return 0; }
 #else
 
 #include <chrono>
@@ -45,7 +43,7 @@
   return (void*)1;
 }
 
-int main() {
+int main(int, char**) {
   pthread_t child_thread;
   std::unique_lock<std::mutex> lk(cv_m);
   pthread_create(&child_thread, 0, test, (void*)0);

test/native/AArch64/ra_sign_state.pass.cpp

diff --git a/test/native/AArch64/ra_sign_state.pass.cpp b/test/native/AArch64/ra_sign_state.pass.cpp
index 35c05fc..dec7aca 100644
--- a/test/native/AArch64/ra_sign_state.pass.cpp
+++ b/test/native/AArch64/ra_sign_state.pass.cpp
@@ -53,7 +53,7 @@
   }
 }
 
-int main() {
+int main(int, char**) {
   try {
     bazz();
   } catch (int i) {