[ELF] Fix creation of segments.

Linker was creating a separate output segment in some cases if input sections
had huge alignments. This patch fixes the issue.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@222974 91177308-0d34-0410-b5e6-96231b3b80d8
[ELF] Rename align2 to alignment.

No change in functionality.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@222975 91177308-0d34-0410-b5e6-96231b3b80d8