make it build for mingw targets

https://bugs.gentoo.org/393573

--- a/bzip2.c
+++ b/bzip2.c
@@ -129,7 +129,7 @@
 #if BZ_LCCWIN32
 #   include <io.h>
 #   include <fcntl.h>
-#   include <sys\stat.h>
+#   include <sys/stat.h>
 
 #   define NORETURN       /**/
 #   define PATH_SEP       '\\'
--- a/bzlib.h
+++ b/bzlib.h
@@ -81,6 +81,9 @@ typedef
       /* windows.h define small to char */
 #      undef small
 #   endif
+#   ifndef WINAPI
+#   define WINAPI
+#   endif
 #   ifdef BZ_EXPORT
 #   define BZ_API(func) WINAPI func
 #   define BZ_EXTERN extern