Currently, __intscan, used by functions like strtol, does not seem to check
for overflow during multiplication.

https://git.musl-libc.org/cgit/musl/tree/src/internal/intscan.c#n69

It at the end checks against the limit, e.g. the size of a long

https://git.musl-libc.org/cgit/musl/tree/src/internal/intscan.c#n90

However, if the value overflows and ends up in the range of the limit,
errno will not be set. It seems that each multiplication operation needs to
be checking for overflow and return errno if it ever happens.