On AIX, NSIG is def'd as SIGMAX64+1, and SIGMAX64 itself is def'd as
255:

```
$ grep -Rw SIGMAX64 /QOpenSys/usr/include/
/QOpenSys/usr/include/sys/signal.h:#define SIGMAX64 255
/QOpenSys/usr/include/sys/signal.h:#define SIGMAX SIGMAX64
/QOpenSys/usr/include/sys/signal.h:#define NSIG64               (SIGMAX64+1)
```

...this causes an overflow when we set num_signals from the value of
NSIG, per GCC:

```
/rpmbuild/BUILD/php-8.5.3/ext/pcntl/pcntl.c:216:25: warning: large integer implicitly truncated to unsigned type [-Woverflow]
  PCNTL_G(num_signals) = NSIG;
                         ^~~~
```

...when we try to use pcntl to i.e. install a signal handler, we get an
error from pcntl:

```
Fatal error: Uncaught ValueError: pcntl_signal(): Argument #1 ($signal) must be less than 0 in phar:///QOpenSys/pkgs/bin/composer/vendor/seld/signal-handler/src/SignalHandler.php:491
```

The easiest way to deal with this silly AIX behaviour is to just promote
the storage size.

…dict

```
Direct leak of 52 byte(s) in 1 object(s) allocated from:
    #0 0x7ff90cd2c161 in malloc (/usr/lib/libasan.so.8+0x12c161) (BuildId: ee5fbab73143ab257a66a33afe0f038a4af7a74e)
    #1 0x55de10c9a468 in tracked_malloc /work/php-8.4/Zend/zend_alloc.c:2973
    #2 0x55de10c99443 in _emalloc /work/php-8.4/Zend/zend_alloc.c:2740
    #3 0x55de102deb86 in zlib_create_dictionary_string /work/php-8.4/ext/zlib/zlib.c:836
    #4 0x55de102e145a in zif_deflate_init /work/php-8.4/ext/zlib/zlib.c:1144
    #5 0x55de10dcac6c in ZEND_DO_ICALL_SPEC_RETVAL_USED_HANDLER /work/php-8.4/Zend/zend_vm_execute.h:1351
    #6 0x55de10f2d69d in execute_ex /work/php-8.4/Zend/zend_vm_execute.h:58907
    #7 0x55de10f41666 in zend_execute /work/php-8.4/Zend/zend_vm_execute.h:64334
    php#8 0x55de110a6cf8 in zend_execute_script /work/php-8.4/Zend/zend.c:1934
    php#9 0x55de10af0ddb in php_execute_script_ex /work/php-8.4/main/main.c:2577
    php#10 0x55de10af128f in php_execute_script /work/php-8.4/main/main.c:2617
    php#11 0x55de110ac5e1 in do_cli /work/php-8.4/sapi/cli/php_cli.c:935
    php#12 0x55de110ae592 in main /work/php-8.4/sapi/cli/php_cli.c:1322
    php#13 0x7ff90c027740  (/usr/lib/libc.so.6+0x27740) (BuildId: 020d6f7c33b2413f4fe10814c4729dce1387f049)
    php#14 0x7ff90c027878 in __libc_start_main (/usr/lib/libc.so.6+0x27878) (BuildId: 020d6f7c33b2413f4fe10814c4729dce1387f049)
    php#15 0x55de10005964 in _start (/work/php-8.4/sapi/cli/php+0x605964) (BuildId: 5f144db4e56ea623e070c56445fb1dfa3f8d085d)

SUMMARY: AddressSanitizer: 52 byte(s) leaked in 1 allocation(s).
```

Closes phpGH-22101.

Depending on the specific PHP configuration, the regex matching for the
version number in get_zlib_version() can fail.
On master, this results in deprecation warnings and subsequent test
borks:
```
Deprecated: version_compare(): Passing null to parameter #1 ($version1) of type string is deprecated in /work/php-src/ext/zlib/tests/gzgetc_basic.skip.php on line 3 [/work/php-src/ext/zlib/tests/gzgetc_basic.phpt]
Deprecated: version_compare(): Passing null to parameter #1 ($version1) of type string is deprecated in /work/php-src/ext/zlib/tests/gzgetc_basic_1.skip.php on line 4
```

Since ZLIB_VERSION is a constant containing the version as a string,
remove all this nonsense and just use the constant directly.