Since we switched from autotools to Meson in commit
94592c1406, we don't need to include
`config.h` early to properly enable large file support. Meson passes
the required macros on the compiler command line instead of defining
them in `config.h`.
This means we can include `config.h` at any time, whenever we want to
check its macros, and there are no ordering constraints.
Don't use FILE_ATTRIBUTE_NORMAL, it's a "magic" value for something
else. To check if a file is a regular file, we need to check if it's
NOT a directory (or a device).
