Correctly handle an ELF symbol defined with "a = b + expr".

We were marking the symbol as absolute instead of computing b's offset + the
expression value.

This fixes pr19126.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203962 91177308-0d34-0410-b5e6-96231b3b80d8
MCContext: Remove redundant assignment

The member variable is not initialized in the ctor so it's already
empty. No need to empty it again.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203963 91177308-0d34-0410-b5e6-96231b3b80d8