Object: Add SF_Executable symbol flag.

This allows us to remove a few uses of IRObjectFile::getSymbolGV() in
llvm-nm.

While here change host-dependent logic in llvm-nm to target-dependent
logic.

Differential Revision: https://reviews.llvm.org/D27075

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@288320 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed