Revert "Revert r363377: [yaml2obj] - Allow setting custom section types for implicit sections."

LLD test case will be fixed in a following commit.

Original commit message:

[yaml2obj] - Allow setting custom section types for implicit sections.

We were hardcoding the final section type for sections that
are usually implicit. The patch fixes that.

This also fixes a few issues in existent test cases and removes
one precompiled object.

Differential revision: https://reviews.llvm.org/D63267

llvm-svn: 363401