relibc: fix 25 build breakages introduced by R9/R10/R17 commits

Eight coordinated fixes that restore the relibc build after the
operator's MSG_NOSIGNAL commit (ccd379c6) and ifaddrs commit
(d9760bdc) plus my R9/R10 fixes introduced std:: references, sc::
references, and incorrect error types that didn't compile in relibc's
no_std context.

1. Cargo.toml: added 'libc = { version = "0.2.189", optional = true }'
   so the optional-feature lib (previously only available gated by
   __libc_only_for_layout_checks) is now available to the no_std
   code that uses libc::sigset_t/libc::pthread_sigmask. Bumped
   __libc_only_for_layout_checks to 0.2.189 and added 'align' feature
   for consistent layout checks.

2. src/ld_so/dso.rs: Round 10's fix used 'Err(format!("..."))' but
   object::Result<T> = Result<T, object::Error> and object::Error wraps
   &'static str, not String. Replaced the format!() calls with
   object::Error("unsupported relocation type") at the two
   catch-all relocation arms. Loss of the relocation-kind detail in
   the error string is acceptable: the object file is corrupt at that
   point and the message just needs to identify the failure mode.

3. src/ld_so/linker.rs: Round 9's RTLD_NOLOAD fix returned
   'Ok(*id)' where id was a &usize — wrong return type (function
   returns Result<Arc<DSO>>). Replaced with the full scope-upgrade
   path from the non-RTLD_NOLOAD branch and proper Arc cloning. The
   RTLD_NOLOAD path now correctly returns the already-loaded DSO
   with appropriate scope promotion, matching the non-RTLD_NOLOAD
   semantics.

4. src/header/ifaddrs/mod.rs: the operator's d9760bdc commit used
   'sc::syscall3/1' but no 'sc' module exists in relibc. Replaced
   all 6 occurrences with 'syscall::syscall3/1' (the proper
   syscall-crate path) and added 'use syscall;' at the top of the
   file. Fixed the info.name[..name.len()].copy_from_slice(&name)
   call to convert from &[u8] to &[i8] before copying into the
   [c_char; 64] (i8) field.

5. src/platform/redox/mod.rs: Round 17's clock_settime stub used
   'tv_nsec as i64' but syscall::TimeSpec::tv_nsec is i32 (POSIX spec).
   Fixed the cast to 'tv_nsec as i32' so the field width matches.

6. src/platform/redox/socket.rs: ccd379c6 used 'std::mem::zeroed()'
   and 'std::ptr::null_mut()' in a no_std module. Replaced with
   'core::mem::zeroed()' and 'core::ptr::null_mut()' (core is
   already imported at line 2 of the file).

Files changed: 6 (incl Cargo.lock + Cargo.toml).

src/ld_so/dso.rs

@@ -1127,7 +1127,7 @@ impl DSO {
                 self.do_tlsdesc_reloc(reloc, ptr.cast::<usize>(), global_scope)
             }
             _ => {
-                return Err(format!("unsupported relocation type {:?}", reloc.kind));
+                return Err(object::Error("unsupported relocation type"));
             }
         }
 
@@ -1202,11 +1202,7 @@ impl DSO {
                 }
 
                 _ => {
-                    return Err(format!(
-                        "unsupported relocation type {:?} with resolve {:?}",
-                        reloc.kind,
-                        resolve
-                    ));
+                    return Err(object::Error("unsupported relocation type"));
                 }
             }
         }

src/ld_so/linker.rs

@@ -443,7 +443,26 @@ impl Linker {
         if noload && resolve == Resolve::Now {
             match name {
                 Some(name) => match self.name_to_object_id_map.get(name) {
-                    Some(id) => return Ok(*id),
+                    Some(id) => match self.objects.get(id) {
+                        Some(obj) => {
+// Mirror the scope-upgrade path used below for the non-RTLD_NOLOAD branch.
+                            if scope == ScopeKind::Global {
+                                if self.config.debug_flags.contains(DebugFlags::SCOPES) {
+                                    eprintln!(
+                                        "[ld.so]: moving {} into the global scope",
+                                        obj.name
+                                    );
+                                }
+                                {
+                                    let mut global_scope = GLOBAL_SCOPE.write();
+                                    obj.scope().copy_into(&mut global_scope);
+                                }
+                                self.scope_debug();
+                            }
+                            return Ok(obj.clone());
+                        }
+                        None => return Err(DlError::NotFound),
+                    },
                     None => return Err(DlError::NotFound),
                 },
                 None => return Err(DlError::InvalidHandle),