Ensure that feature code paths are well-tested

Compilers and standard libraries are inconsistent about the values of feature macros and such. It would be good to have a way to definitely turn on certain code paths for test. See https://github.com/intel/cpp-std-extensions/pull/116 for an example of how this fails.

未指定任何檔案或測試進入點。首先比較 pull request #116 中描述的失敗，並追蹤它所執行的 feature-macro 決策。定義一種可重複的方法，在測試期間強制執行選定的程式碼路徑，然後驗證該方法在 issue 所描述的編譯器與標準函式庫組合中都有效。

由索引模型根據 Issue 內容生成。