ext/pcntl: Bump num_signals to uint16_t

[NattyNarwhal]

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.

[devnexen]

looks safe change, did you have a quick look with pahole or similar ?

[NattyNarwhal]

I haven't used pahole, no. I'm guessing this does slightly blow up the size of the structure, as the bools and previous uint8 would have been packed into 32 bits.