MC: Extract a derived class from ELFObjectWriter. NFCI.
MC: Extract a derived class from ELFObjectWriter. NFCI.

This class will be used to create regular, non-split ELF files.

Part of PR37466.

Differential Revision: https://reviews.llvm.org/D47049

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@332870 91177308-0d34-0410-b5e6-96231b3b80d8

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