bug#49261: Segfault during loadup

[Eli Zaretskii]

> Date: Sun, 11 Jul 2021 13:21:16 +0300
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: larsi@gnus.org, 49261@debbugs.gnu.org
> 
> Thanks, but these changes don't cater to 32-bit builds --with-wide-int:
> 
>     CC       alloc.o
>   In file included from alloc.c:33:
>   alloc.c: In function 'mark_maybe_pointer':
>   lisp.h:251:18: warning: unsigned conversion from 'long long int' to 
> 'uintptr_t' {aka 'unsigned int'} changes value from '2305843009213693951' to 
> '4294967295' [-Woverflow]
>     251 | # define VALMASK (USE_LSB_TAG ? - (1 << GCTYPEBITS) : VAL_MAX)
>       |                  ^
>   alloc.c:4767:24: note: in expansion of macro 'VALMASK'
>    4767 |       uintptr_t mask = VALMASK;
>       |                        ^~~~~~~

I tried to fix this on master, please take a look.