Have not found a universal way to detect C11 and after some deliberation
__BIONIC__ seems to be a better choice for these cases.

Fix build error because DTTOIF function is not available.

If we were using C++17, we could use [[fallthrough]] instead... but we are not.

MinGW 7.2 (x86_64) build failed

The disk-backed implementations were already inherently threadsafe. Making this explicit allows callers to rely on it.

This is particularly useful for SchemaParser, which is intended to be threadsafe.

Apparently, msync()'s parameters must be page-aligned, bah.

This allows detecting when two objects point to the same underlying file.

Just a random thing I noticed.

Windows support will be implemented in a separate file.