Define DbiStreamBuilder::addSectionContribs.
This patch defines a new function to add a SectionContribs stream
to a PDB file. Unlike SectionMap, SectionContribs contains a list
of input sections as opposed to output sections.
Note that this patch needs improving because currently we do not
set Module field in SectionContribs entries. In a follow-up patch,
I'll add Modules and then fix it after that.
Differential Revision: https://reviews.llvm.org/D26210
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@286677
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