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

No functional change, no code review.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@292434 91177308-0d34-0410-b5e6-96231b3b80d8

test/support/filesystem_test_helper.hpp

@@ -381,7 +381,7 @@ bool checkCollectionsEqualBackwards(
 }
 
 // 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);