Is this change still required even if we bump MIN_WINNT to 0x0600 for all the environments that include win32.h?
Right now we are ifdefing that code out for MinGW, so it's not a visible issue, but it'll be when we do.
At the end, this would mean dropping support for Windows XP and Windows Server 2003 as run-time environments as listed in [1], which are not supported officially since 2014 (even if there have been some patches for some critical issues). So I'd be fine to raise the bar for v16~, particularly as this would allow us to get rid of this code related to locales.
Even Windows Server 2008 [1] is at its End of Life, so this should surprise no one.