Use the entire word in ptrace_get_vec_len() and ptrace_read_vec().

For compat binaries, use the upper 32-bits as the next word instead
of calling ptrace(2) to get it.  This reduces the number of ptrace(2)
calls when reading argv and envp for compat binaries.

src/exec_ptrace.h

@@ -231,8 +231,7 @@ struct sudo_ptrace_regs {
 	struct compat_user_pt_regs compat;
 #endif
     } u;
-    unsigned long wordsize;
-    unsigned long addrmask;
+    unsigned int wordsize;
     bool compat;
 };