fix(library/process): do not strip signal information from child exit status

This should match the meaning of "$?" in bash:

"3.7.5 Exit Status

The exit status of an executed command is the value returned by the waitpid system call or equivalent function. Exit statuses fall between 0 and 255."

Fixes #1868

src/library/process.cpp

@@ -324,7 +324,7 @@ struct unix_child : public child {
     unsigned wait() override {
         int status;
         waitpid(m_pid, &status, 0);
-        return static_cast<unsigned>(WEXITSTATUS(status));
+        return static_cast<unsigned>(status);
     }
 };