Fix type mismatch between get_crc_table() and crc_table.

crc_table is made using a four-byte integer (when that can be
determined).  However get_crc_table() returned a pointer to an
unsigned long, which could be eight bytes.  This fixes that by
creating a new z_crc_t type for the crc_table.

This type is also used for the BYFOUR crc calculations that depend
on a four-byte type.  The four-byte type can now be determined by
./configure, which also solves a problem where ./configure --solo
would never use BYFOUR.  No the Z_U4 #define indicates that four-
byte integer was found either by ./configure or by zconf.h.

zconf.h.cmakein

@@ -390,6 +390,29 @@ typedef uLong FAR uLongf;
    typedef Byte       *voidp;
 #endif
 
+/* ./configure may #define Z_U4 here */
+
+#if !defined(Z_U4) && !defined(Z_SOLO) && defined(STDC)
+#  include <limits.h>
+#  if (UINT_MAX == 0xffffffffUL)
+#    define Z_U4 unsigned
+#  else
+#    if (ULONG_MAX == 0xffffffffUL)
+#      define Z_U4 unsigned long
+#    else
+#      if (USHRT_MAX == 0xffffffffUL)
+#        define Z_U4 unsigned short
+#      endif
+#    endif
+#  endif
+#endif
+
+#ifdef Z_U4
+   typedef Z_U4 z_crc_t;
+#else
+   typedef unsigned long z_crc_t;
+#endif
+
 #ifdef HAVE_UNISTD_H    /* may be set to #if 1 by ./configure */
 #  define Z_HAVE_UNISTD_H
 #endif