NOTE.todo

1. Making code and data separation reliable. Due to it is not reliable yet, this feature is
  disabled.

2. Checking if a pointer is already encrypted before invoking the encryption routine. If it isi
  already encrypted, skip the encryption routine.
    - Solution1: maintain a table in data segment of each module. Its entry contains a 4-bytes
      value indicating if a pointer is already encrypted and (if yes) the offset into the rand
      mapping table. The relative address of pointer definition (e.g., getpc) into its entry
      in the table is fixed, so that the checking can efficiently locate the corresponding 
      entry at runtime.
    - Solution2: use a hash table for the random mapping table

3. Prebuild libraries.
    - Due to that some projects (e.g., gcc) have custom building approaches, there may have
      difficulties in building them with ASLR-Guard's toolchain, so we will prebuild them for
      direct use.