select: fix 64-bit timeout truncation on pre-time64 kernels

If the (normalized) timeout passed to select exceeds INT_MAX seconds on
an arch with SYS_pselect6_time64 and the kernel is too old to support
time64 syscalls, the timeout is implicitly converted to (32-bit) long on
the fallback path, losing its upper 32 bits and potentially becoming a
small positive value, violating the intended semantics, or even
a negative value, causing the fallback syscall failure. Fix this by
saturating the timeout at INT_MAX as done in other time64 fallback
cases.

src/select/select.c

@@ -33,6 +33,7 @@ int select(int n, fd_set *restrict rfds, fd_set *restrict wfds, fd_set *restrict
 			((syscall_arg_t[]){ 0, _NSIG/8 }));
 	if (SYS_pselect6 == SYS_pselect6_time64 || r!=-ENOSYS)
 		return __syscall_ret(r);
+	s = CLAMP(s);
 #endif
 #ifdef SYS_select
 	return syscall_cp(SYS_select, n, rfds, wfds, efds,