util: Add a Win32 futex impl

This uses APIs that are not available on Win7. Since this is a build-time
configuration, and since we can't use the SDK version as an indicator
(since you can support Win7 via new SDKs), a new option is added to allow
disabling it, to maintain Win7 support if desired.

Reviewed-by: Jose Fonseca <jfonseca@vmware.com>
Reviewed-by: Yonggang Luo <luoyonggang@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17431>

meson_options.txt

@@ -547,4 +547,12 @@ option(
   type : 'string',
   value : '',
   description : 'Override build id for shader cache keys (hex string). Can be extracted with readelf -x .note.gnu.build-id'
-)
+)
+option(
+  'min-windows-version',
+  type : 'integer',
+  min : 7,
+  max : 11,
+  value : 8,
+  description : 'Minimum Windows version to support. Defaults to Windows 8.'
+)