libobs/util: Add get_win_ver_int() func (windows)

Returns the current version number of windows.  The lowest byte is the
minor version number, then the next lowest byte is the major version
number.  E.g. 0x601 for Windows 7, 0x602 for Windows 8, 0x603 for
Windows 8.1, and 0xA00 for Windows 10.

libobs/util/windows/win-version.h

@@ -32,6 +32,7 @@ struct win_version_info {
 EXPORT bool is_64_bit_windows(void);
 EXPORT bool get_dll_ver(const wchar_t *lib, struct win_version_info *info);
 EXPORT void get_win_ver(struct win_version_info *info);
+EXPORT uint32_t get_win_ver_int(void);
 
 #ifdef __cplusplus
 }