[X86] Reland D71360 Clean up UseInitArray initialization for X86ELFTargetObjectFile

UseInitArray is now the CC1 default but TargetLoweringObjectFileELF::UseInitArray still defaults to false.
The following two unknown OS target triples continue using .ctors/.dtors because InitializeELF is not called.

clang -target i386 -c a.c
clang -target x86_64 -c a.c

This cleanup fixes this as a bonus.

Differential Revision: https://reviews.llvm.org/D71360