Build system: configure: add AC_TYPE_SSIZE_T

Invoke `AC_TYPE_SSIZE_T` to provide a suitable typedef for `ssize_t` in case
the system doesn't define it (MVSC?).


git-svn-id: https://svn.code.sf.net/p/vice-emu/code/trunk@45165 379a1393-f5fb-40a0-bcee-ef074d9b53f7

vice/configure.ac

@@ -423,6 +423,8 @@ AM_PROG_AS
 
 dnl Other build environment checks
 AC_SYS_LARGEFILE
+AC_TYPE_SSIZE_T
+
 
 AC_CONFIG_HEADERS([src/config.h])