Add back gz_intmax for zlib compatibility when linking statically

gzguts.h

@@ -135,11 +135,12 @@ typedef gz_state *gz_statep;
 
 /* shared functions */
 void Z_INTERNAL gz_error(gz_state *, int, const char *);
-
+#ifdef ZLIB_COMPAT
+unsigned Z_INTERNAL gz_intmax(void);
+#endif
 /* GT_OFF(x), where x is an unsigned value, is true if x > maximum z_off64_t
    value -- needed when comparing unsigned to z_off64_t, which is signed
    (possible z_off64_t types off_t, off64_t, and long are all signed) */
-unsigned Z_INTERNAL gz_intmax(void);
 #define GT_OFF(x) (sizeof(int) == sizeof(z_off64_t) && (x) > INT_MAX)
 
 #endif /* GZGUTS_H_ */

gzlib.c

@@ -524,20 +524,8 @@ void Z_INTERNAL gz_error(gz_state *state, int err, const char *msg) {
     (void)snprintf(state->msg, strlen(state->path) + strlen(msg) + 3, "%s%s%s", state->path, ": ", msg);
 }
 
-/* portably return maximum value for an int (when limits.h presumed not
+#ifdef ZLIB_COMPAT
-   available) -- we need to do this to cover cases where 2's complement not
-   used, since C standard permits 1's complement and sign-bit representations,
-   otherwise we could just use ((unsigned)-1) >> 1 */
 unsigned Z_INTERNAL gz_intmax(void) {
-#ifdef INT_MAX
     return INT_MAX;
-#else
-    unsigned p = 1, q;
-    do {
-        q = p;
-        p <<= 1;
-        p++;
-    } while (p > q);
-    return q >> 1;
-#endif
 }
+#endif

zlib.map

@@ -13,6 +13,7 @@ ZLIB_1.2.0 {
     zcfree;
     z_errmsg;
     gz_error;
+    gz_intmax;
     _*;
 };