[libc++] Fix signature of main() in tests

Otherwise, this breaks freestanding builds, where `main()` isn't mangled
specially and we need to assume that we have a `int main(int, char**)`
entry point in each test for things to work.

libcxx/test/std/utilities/tuple/tuple.tuple/tuple.assign/const_convert_copy.pass.cpp

@@ -74,7 +74,7 @@ constexpr bool test() {
   return true;
 }
 
-int main() {
+int main(int, char**) {
   test();
 
 // gcc cannot have mutable member in constant expression

libcxx/test/std/utilities/tuple/tuple.tuple/tuple.assign/const_convert_move.pass.cpp

@@ -73,7 +73,7 @@ constexpr bool test() {
   return true;
 }
 
-int main() {
+int main(int, char**) {
   test();
 
 // gcc cannot have mutable member in constant expression

libcxx/test/std/utilities/tuple/tuple.tuple/tuple.assign/const_copy.pass.cpp

@@ -66,7 +66,7 @@ constexpr bool test() {
   return true;
 }
 
-int main() {
+int main(int, char**) {
   test();
 
 // gcc cannot have mutable member in constant expression

libcxx/test/std/utilities/tuple/tuple.tuple/tuple.assign/const_move.pass.cpp

@@ -69,7 +69,7 @@ constexpr bool test() {
   return true;
 }
 
-int main() {
+int main(int, char**) {
   test();
 // gcc cannot have mutable member in constant expression
 #if !defined(TEST_COMPILER_GCC)

libcxx/test/std/utilities/tuple/tuple.tuple/tuple.assign/const_pair_copy.pass.cpp

@@ -78,7 +78,7 @@ constexpr bool test() {
   return true;
 }
 
-int main() {
+int main(int, char**) {
   test();
 
 // gcc cannot have mutable member in constant expression

libcxx/test/std/utilities/tuple/tuple.tuple/tuple.assign/const_pair_move.pass.cpp

@@ -78,7 +78,7 @@ constexpr bool test() {
   return true;
 }
 
-int main() {
+int main(int, char**) {
   test();
 
 // gcc cannot have mutable member in constant expression

libcxx/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc_const_move_pair.pass.cpp

@@ -106,7 +106,7 @@ constexpr bool test() {
   return true;
 }
 
-int main() {
+int main(int, char**) {
   test();
   static_assert(test());
 

libcxx/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/alloc_non_const_pair.pass.cpp

@@ -103,7 +103,7 @@ constexpr bool test() {
   return true;
 }
 
-int main() {
+int main(int, char**) {
   test();
   static_assert(test());
 

libcxx/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/const_move_pair.pass.cpp

@@ -85,7 +85,7 @@ constexpr bool test() {
   return true;
 }
 
-int main() {
+int main(int, char**) {
   test();
   static_assert(test());
 

libcxx/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/non_const_pair.pass.cpp

@@ -84,7 +84,7 @@ constexpr bool test() {
   return true;
 }
 
-int main() {
+int main(int, char**) {
   test();
   static_assert(test());