Fix unicode filename compare when wchar_t is not 16bit

Do not use wcscmp() which takes wchar_t arguments.
wchar_t bit width is system dependent. It is often 32bits.
Grafx2 supports 16bits wide characters

fixes b49fa1dfcc

src/filesel.c

@@ -827,7 +827,7 @@ void Read_list_of_drives(T_Fileselector *list, byte name_length)
 #else
 // case-sensitive
   #define FILENAME_COMPARE strcmp
-  #define FILENAME_COMPARE_UNICODE wcscmp
+  #define FILENAME_COMPARE_UNICODE Unicode_strcmp
 #endif