[gold] Ignore bitcode from sections inside object files

-fembed-bitcode will put bitcode into special sections within object
files, but this is not meant to be used by LTO, so the gold plugin
should ignore it.

https://github.com/llvm/llvm-project/issues/47216

Reviewed By: tejohnson, MaskRay

Differential Revision: https://reviews.llvm.org/D116995