bzlib.h: Move #includes outside extern "C" {...}

This helps C++ compilers that come with their own standard library
headers that don't expect to be included inside of extern "C" {...}.

https://sourceware.org/bugzilla/show_bug.cgi?id=32812

bzlib.h

@@ -22,6 +22,15 @@
 #ifndef _BZLIB_H
 #define _BZLIB_H
 
+#ifndef BZ_NO_STDIO
+/* Need a definitition for FILE */
+#include <stdio.h>
+#endif
+
+#ifdef _WIN32
+#include <windows.h>
+#endif
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -70,13 +79,7 @@ typedef
 #define BZ_EXPORT
 #endif
 
-#ifndef BZ_NO_STDIO
-/* Need a definitition for FILE */
-#include <stdio.h>
-#endif
-
 #ifdef _WIN32
-#   include <windows.h>
 #   ifdef small
       /* windows.h define small to char */
 #      undef small