Fix a couple of issues in MSVC related to min and max.

MSVC apparently thinks that the result of arithmetic promotions
on an `unsigned:4` bitfield is `unsigned`, not `int`; which then
causes it to fail to deduce whether the `T` in `min<T>` should be
`unsigned` (the type of the LHS) or `int` (the type of the RHS).
Clang and GCC agree that the result of arithmetic promotions on
an `unsigned:4` bitfield should be `int`, so they don't see any
ambiguity here.

sysconfig.h

@@ -253,6 +253,7 @@
 #if ISWINDOWS
 #define hyper fake_hyper // avoid "hyper" typedef in <_mingw.h>
 #define WIN32_LEAN_AND_MEAN // avoid "rad1" macro in <windows.h>
+#define NOMINMAX // avoid "min" and "max" macros in <windows.h>
 #endif
 
 #include <stdio.h>