bug#73835: Build failure with gcc 14 and musl on 32 bit

Hi,

I get this error message when compiling guile 3.0.9 and 3.0.10 with gcc
14 / musl libc on 32 bit Alpine Linux:

filesys.c: In function 'scm_sendfile':
filesys.c:1405:16: error: assignment to 'off_t *' {aka 'long long int *'} from incompatible pointer type 'scm_t_off *' {aka 'long int *'} [-Wincompatible-pointer-types]
 1405 |     offset_ptr = SCM_UNBNDP (offset) ? NULL : &c_offset;
      |                ^

It looks like an assumption that off_t is 32 bit, which is not true on musl libc.

-nc