Small cleanups for copy_file sendfile fix (#544)

* copy_file() - fix preprocessor comments in sendfile cleanup

* copy_file() - deduplicate call to fchmod

* check for fchmod failure

* clang-format/messages

Co-authored-by: Billy Robert O'Neal <bion@microsoft.com>

src/vcpkg/base/files.cpp

@@ -2896,7 +2896,11 @@ namespace vcpkg
 
             // fcopyfile copies the mode so no need to fchmod here
             return true;
-#else
+#else // ^^^ (defined(__APPLE__) // !defined(__APPLE__) vvv
+
+            destination_fd.fchmod(source_stat.st_mode, ec);
+            if (ec) return false;
+
 #if defined(__linux__)
             // https://man7.org/linux/man-pages/man2/sendfile.2.html#NOTES
             // sendfile() will transfer at most 0x7ffff000 (2,147,479,552)
@@ -2924,14 +2928,10 @@ namespace vcpkg
                 remaining_size -= this_send_actual;
             }
 
-            if (!ec)
-            {
-                destination_fd.fchmod(source_stat.st_mode, ec);
-                return true;
-            }
+            if (!ec) return true;
             // Else fall back to read/write
             ec.clear();
-#endif // ^^^ !(defined(__APPLE__) || defined(__linux__))
+#endif // ^^^ defined(__linux__)
 
             constexpr std::size_t buffer_length = 4096;
             unsigned char buffer[buffer_length];
@@ -2957,7 +2957,6 @@ namespace vcpkg
                 }
             }
 
-            destination_fd.fchmod(source_stat.st_mode, ec);
             return !ec;
 #endif // ^^^ !(defined(__APPLE__)
 #endif // ^^^ !_WIN32