[libc++] Add `return 0` to some main() functions

This unbreaks the tests when running in freestanding mode.

3 files changed, 3 insertions, 0 deletions

diff --git a/libcxx/test/std/utilities/optional/optional.monadic/and_then.pass.cpp b/libcxx/test/std/utilities/optional/optional.monadic/and_then.pass.cpp
index b2de9c7188db..61c61ff73785 100644
--- a/libcxx/test/std/utilities/optional/optional.monadic/and_then.pass.cpp
+++ b/libcxx/test/std/utilities/optional/optional.monadic/and_then.pass.cpp
@@ -259,4 +259,5 @@ constexpr bool test() {
 int main(int, char**) {
   test();
   static_assert(test());
+  return 0;
 }
diff --git a/libcxx/test/std/utilities/optional/optional.monadic/or_else.pass.cpp b/libcxx/test/std/utilities/optional/optional.monadic/or_else.pass.cpp
index 2d9a81ac883c..ccc94ab9be2c 100644
--- a/libcxx/test/std/utilities/optional/optional.monadic/or_else.pass.cpp
+++ b/libcxx/test/std/utilities/optional/optional.monadic/or_else.pass.cpp
@@ -69,4 +69,5 @@ constexpr bool test() {
 int main(int, char**) {
   test();
   static_assert(test());
+  return 0;
 }
diff --git a/libcxx/test/std/utilities/optional/optional.monadic/transform.pass.cpp b/libcxx/test/std/utilities/optional/optional.monadic/transform.pass.cpp
index 59c559d149af..209c8a34da05 100644
--- a/libcxx/test/std/utilities/optional/optional.monadic/transform.pass.cpp
+++ b/libcxx/test/std/utilities/optional/optional.monadic/transform.pass.cpp
@@ -202,4 +202,5 @@ constexpr bool test() {
 int main(int, char**) {
   test();
   static_assert(test());
+  return 0;
 }