Windows 10 SDK build fixes

Build without Win32.mak, and using Universal C Runtime (UCRT)

windows: Check for APPVER, not VCVER for UCRT

When deciding whether UCRT is used (and thus no CRT merge modules), check for
Windows 10 rather than the version of Visual Studio, as we may be building with
an older SDK.

include/config.h.w32

@@ -887,6 +887,17 @@ static const char *const rcsid[] = { (const char *)rcsid, "@(#)" msg }
 /* Define if you have the function `strtok_r'. */
 /* #define HAVE_STRTOK_R 1 */
 
+#if defined(__has_include)
+# if __has_include(<corecrt.h>)
+#  define HAVE_UCRT 1
+# endif
+#endif
+
+#ifdef HAVE_UCRT
+#define HAVE_STRTOLL 1
+#define HAVE_STRTOULL 1
+#endif
+
 /* Define to 1 if the system has the type `struct addrinfo'. */
 #define HAVE_STRUCT_ADDRINFO 1