Fix invalid memory access on android x86

On certain versions of android x86, the main module `app_process` is not
built as PIE.  When accessing the PT_GNU_EH_FRAME_HDR in such a
scenario, the `dlpi_addr` is 0, but the virtual address is not
relocated.  Manually rebase the address to avoid an invalid memory
access.

llvm-svn: 299575