Convert a member variable to a local variable. NFC.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224311 91177308-0d34-0410-b5e6-96231b3b80d8
Remove the last unnecessary member variable of mapped_file_region. NFC.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224312 91177308-0d34-0410-b5e6-96231b3b80d8