dev-util/b2: fix crash on Apple M1 due to undefined behavior.

Currently, the build system dev-util/b2-4.9.3, notably used
by Boost, crashes on Apple M1 w/ macOS with a Segmentation
Fault. This prevents one from using the tool, and also making
building Boost impossible. It's also notable since it contains
the keyword "~x64-macos", so it should receive first-class
macOS support.

It has been determined that when the NULL-terminated variadic
function call_rule() is invoked, the value 0 is passed as the
last argument to act as a terminator. However, this is an
integer value, which is incompatible with the pointer data type
expected by call_rule().

This is undefined behavior in C, correct operation is not guaranteed.
In fact, it causes b2 to crash on Apple M1 when GCC is used - the
loop is not terminated when it should, instead, it keeps
running, creating the following error:

    lol_add failed due to reached limit of 19 elements

In some cases, it can even corrupt the internal state of the
program, creating an infinite loop.

This commit fixes the problem by explicitly casting the value 0
to the correct pointer type (OBJECT *).

Since the existence of the bug doesn't prevent one from installing
the package, it can lurk inside the system and remain undetected,
furthermore, it's technically a C programming bug, other platforms
could've been affected as well in theory. Thus, we also bump the
package version.

Closes: https://bugs.gentoo.org/895524
Signed-off-by: Yifeng Li <tomli@tomli.me>
Closes: https://github.com/gentoo/gentoo/pull/29681
Signed-off-by: Sam James <sam@gentoo.org>

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