[libcxx] [test] Fix comment typos, strip trailing whitespace.

No functional change, no code review.

llvm-svn: 292434
diff --git a/libcxx/test/support/filesystem_test_helper.hpp b/libcxx/test/support/filesystem_test_helper.hpp
index c2e41fc..6cc0e37 100644
--- a/libcxx/test/support/filesystem_test_helper.hpp
+++ b/libcxx/test/support/filesystem_test_helper.hpp
@@ -381,7 +381,7 @@
 }
 
 // We often need to test that the error_code was cleared if no error occurs
-// this function returns a error_code which is set to an error that will
+// this function returns an error_code which is set to an error that will
 // never be returned by the filesystem functions.
 inline std::error_code GetTestEC() {
     return std::make_error_code(std::errc::address_family_not_supported);