gdatetime.c: Fix MSVC builds for lack of NAN items
Hi,
This will apply for the master and glib-2-66 branches, but I will post this for glib-2-66 since we don't want to bump compiler requirements within a stable cycle, and we can decide whether we want to bump compiler requirements for the master branch.
From the commit message: Use a fallback for isnan() on Visual Studio 2012 or earlier, and define NAN if it does not exist.
With blessings, thank you!