checkpoint: fix memfd_create c_char portability; drop m1/em-dash from build warnings

Signed-off-by: Cong Wang <cwang@multikernel.io>

Author: congwang-mk

crates/sandlock-core/build.rs

@@ -13,7 +13,7 @@ fn main() {
         &repo_root.join("tests/rootfs-helper"),
         &["musl-gcc", "cc"],
         &["-static", "-O2"],
-        "cannot compile tests/rootfs-helper — chroot tests will fail. \
+        "cannot compile tests/rootfs-helper: chroot tests will fail. \
          Install musl-tools or static libc.",
     );
 
@@ -29,7 +29,7 @@ fn main() {
         &stub_bin,
         &["cc"],
         &["-static", "-nostdlib", "-no-pie", "-O2"],
-        "cannot compile restore-stub — M1 restore-stub tests will be skipped.",
+        "cannot compile restore-stub: its restore tests will be skipped.",
     );
     // Emit the path every run (rustc-env is not cached across build-script runs),
     // whether or not the binary was just (re)built.

crates/sandlock-core/src/checkpoint/restore-stub.c

@@ -1,5 +1,5 @@
 /*
- * restore-stub — freestanding self-restore stub (x86_64).
+ * restore-stub: freestanding self-restore stub (x86_64).
  *
  * This is a core component of the checkpoint restore engine, not a test
  * fixture: the supervisor execs this stub into a fresh, fully-sandboxed process

crates/sandlock-core/tests/integration/test_restore_stub.rs

@@ -115,7 +115,7 @@ fn eventfd() -> RawFd {
 
 fn memfd_with(bytes: &[u8]) -> RawFd {
     let name = b"restore-blob\0";
-    let fd = unsafe { libc::memfd_create(name.as_ptr() as *const i8, 0) } as i32;
+    let fd = unsafe { libc::memfd_create(name.as_ptr() as *const libc::c_char, 0) } as i32;
     assert!(fd >= 0, "memfd_create");
     let mut off = 0usize;
     while off < bytes.len() {