[ELF] Emit zeroFill as STT_OBJECT in the final executable. ld does this.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@171704 91177308-0d34-0410-b5e6-96231b3b80d8
[ELF] Remove dead variable.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@171707 91177308-0d34-0410-b5e6-96231b3b80d8
[ELF] Change Segment to hold Chunks instead of Sections. No functionality change.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@171708 91177308-0d34-0410-b5e6-96231b3b80d8
[ELF] Emit the file header and program headers at the beginning of the first segment.

This is required for the loader to correctly set AT_PHDR.

With this lld can correctly link against dietlibc and get to main.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@171709 91177308-0d34-0410-b5e6-96231b3b80d8