[ELF] - Linkerscript: create multiple output sections for inputs with different attributes.

Previously we combined sections by name if linkerscript was used.
For that we had to disable SHF_MERGE handling temporarily, but then
found that implementing it properly will require additional complexity layers like
subsections or something.
At the same time looks we can live with multiple output sections approach for now.
That patch do this change.

Differential revision: https://reviews.llvm.org/D24127

llvm-svn: 280801