Meson configure does not currently find functions that would require higher (than what ever is the minimum with msys2 headers) Windows version. To change that, set _WIN32_WINNT for these checks (they ignore global options where it's currently set), so they know that functions available only in later Windows versions suffice.
This is not needed - premises turned out to be false. Function search is interested about the library files only. It doesn't care about headers, and how they are parsed, at all.
Meson configure does not currently find functions that would require higher (than what ever is the minimum with msys2 headers) Windows version. To change that, set _WIN32_WINNT for these checks (they ignore global options where it's currently set), so they know that functions available only in later Windows versions suffice.