Windows fixes from Kohei Yoshida:
- remove ZIP_EXTERN from functions not (yet?) part of public API
- provide fallback definition of ssize_t

Left to do:
- provide fallback definition of PRId64, PRIu64
- add getopt.c to regress programs when needed

cmake-config.h.in

diff --git a/cmake-config.h.in b/cmake-config.h.in
index ae731c2..3067607 100644
--- a/cmake-config.h.in
+++ b/cmake-config.h.in
@@ -10,4 +10,23 @@
 #cmakedefine HAVE_UNISTD_H
 #define PACKAGE "@PACKAGE@"
 #define VERSION "@VERSION@"
+
+#cmakedefine HAVE_SSIZE_T
+#cmakedefine SIZE_T_LIBZIP ${SIZE_T_LIBZIP}
+#cmakedefine INT_LIBZIP ${INT_LIBZIP}
+#cmakedefine LONG_LIBZIP ${LONG_LIBZIP}
+#cmakedefine LONGLONG_LIBZIP ${LONGLONG_LIBZIP}
+
+#ifndef HAVE_SSIZE_T
+#  if SIZE_T_LIBZIP == INT_LIBZIP
+typedef int ssize_t
+#  elif SIZE_T_LIBZIP == LONG_LIBZIP
+typedef long ssize_t
+#  elif SIZE_T_LIBZIP == LONG_LONG_LIBZIP
+typedef long long ssize_t
+#  elif
+#error no suitable type for ssize_t found
+#  endif
+#endif
+
 #endif /* HAD_CONFIG_H */