core.stdc.stdint: Fix int_fast8_t alias for Win64

Author: kinke

src/core/stdc/stdint.d

@@ -63,10 +63,7 @@ version (Windows)
     alias int_least64_t  = long;     ///
     alias uint_least64_t = ulong;    ///
 
-    version (Win64) // TODO: this is wrong but tested in compilable/teststdint.d
-        alias int_fast8_t = char;   ///
-    else
-        alias int_fast8_t = byte;   ///
+    alias int_fast8_t   = byte;     ///
     alias uint_fast8_t  = ubyte;    ///
     alias int_fast16_t  = int;      ///
     alias uint_fast16_t = uint;     ///