Handle Error::NOSYS in tests for Linux-specific syscalls.

Linux 2.6.32 doesn't support `prlimit64` or `memfd_create`, so handle
`Error::NOSYS` gracefully in tests.

Author: sunfishcode

tests/io/seals.rs

@@ -5,7 +5,11 @@ use std::io::Write;
 
 #[test]
 fn test_seals() {
-    let fd = memfd_create("test", MemfdFlags::CLOEXEC | MemfdFlags::ALLOW_SEALING).unwrap();
+    let fd = match memfd_create("test", MemfdFlags::CLOEXEC | MemfdFlags::ALLOW_SEALING) {
+        Ok(fd) => fd,
+        Err(rustix::io::Error::NOSYS) => return,
+        Err(err) => Err(err).unwrap(),
+    };
     let mut file = File::from_fd(fd.into());
 
     writeln!(&mut file, "Hello!").unwrap();

tests/process/rlimit.rs

@@ -26,7 +26,11 @@ fn test_prlimit() {
 
     let first = rustix::process::getrlimit(Resource::Core);
 
-    let old = rustix::process::prlimit(None, Resource::Core, new.clone()).unwrap();
+    let old = match rustix::process::prlimit(None, Resource::Core, new.clone()) {
+        Ok(rlimit) => rlimit,
+        Err(rustix::io::Error::NOSYS) => return,
+        Err(e) => Err(e).unwrap(),
+    };
 
     assert_eq!(first, old);