Fix zlib implicit declarations

Author: HexDecimal

build_libtcod.py

@@ -180,8 +180,8 @@ def walk_sources(directory: str) -> Iterator[str]:
     include_dirs.append("libtcod/src/zlib/")
 
 
-if sys.platform == "darwin":
-    # Fix "implicit declaration of function 'close'" in zlib.
+if sys.platform != "win32":
+    # Fix implicit declaration of multiple functions in zlib.
     define_macros.append(("HAVE_UNISTD_H", 1))