[libcxx] [test] Add (void) return casts on functions marked nodiscard in MS STL

Differential Revision: https://reviews.llvm.org/D89533

libcxx/test/std/input.output/filesystems/fs.op.funcs/fs.op.canonical/canonical.pass.cpp

@@ -98,7 +98,7 @@ TEST_CASE(test_exception_contains_paths)
     CWDGuard guard;
     const path p = "blabla/dne";
     try {
-        canonical(p);
+        (void)canonical(p);
         TEST_REQUIRE(false);
     } catch (filesystem_error const& err) {
         TEST_CHECK(err.path1() == p);
@@ -107,7 +107,7 @@ TEST_CASE(test_exception_contains_paths)
     }
     fs::current_path(static_env.Dir);
     try {
-        canonical(p);
+        (void)canonical(p);
         TEST_REQUIRE(false);
     } catch (filesystem_error const& err) {
         TEST_CHECK(err.path1() == p);

libcxx/test/std/input.output/filesystems/fs.op.funcs/fs.op.copy_file/copy_file.pass.cpp

@@ -101,7 +101,7 @@ TEST_CASE(test_attributes_get_copied) {
   scoped_test_env env;
   const path file = env.create_file("file1", 42);
   const path dest = env.make_env_path("file2");
-  auto st = status(file);
+  (void)status(file);
   perms new_perms = perms::owner_read;
   permissions(file, new_perms);
   std::error_code ec = GetTestEC();

libcxx/test/std/input.output/filesystems/fs.op.funcs/fs.op.read_symlink/read_symlink.pass.cpp

@@ -41,7 +41,7 @@ TEST_CASE(test_error_reporting)
     {
 #ifndef TEST_HAS_NO_EXCEPTIONS
         try {
-            fs::read_symlink(f);
+            (void)fs::read_symlink(f);
             return false;
         } catch (filesystem_error const& err) {
             return err.path1() == f

libcxx/test/std/input.output/filesystems/fs.op.funcs/fs.op.space/space.pass.cpp

@@ -49,7 +49,7 @@ TEST_CASE(test_error_reporting)
     {
 #ifndef TEST_HAS_NO_EXCEPTIONS
         try {
-            space(f);
+            (void)space(f);
             return false;
         } catch (filesystem_error const& err) {
             return err.path1() == f