Rename wrongly named field sval to rval.

`__c_anonymous_ptrace_syscall_info_exit` field was wrongly named `sval` instead of `rval`. Fix it by renaming the field.

Author: Marcondiro

src/unix/linux_like/linux/gnu/mod.rs

@@ -172,7 +172,7 @@ s! {
     }
 
     pub struct __c_anonymous_ptrace_syscall_info_exit {
-        pub sval: crate::__s64,
+        pub rval: crate::__s64,
         pub is_error: crate::__u8,
     }