improve handling of IOExceptions in JavaCompiler.close()

Seen in JavaCompiler.close()

            for (Closeable c: closeables) {
                try {
                    c.close();
                } catch (IOException e) {
                    // When javac uses JDK 7 as a baseline, this code would be
                    // better written to set any/all exceptions from all the
                    // Closeables as suppressed exceptions on the FatalError
                    // that is thrown.
                    JCDiagnostic msg = diagFactory.fragment(Fragments.FatalErrCantClose);
                    throw new FatalError(msg, e);
                }
            }

Since the baseline is now up to 11, we could refactor the code qas suggested in the comment.