[Driver] Infer the correct option to ld64 for -fembed-bitcode

Summary:
-fembed-bitcode infers -bitcode_bundle to ld64 but it is not correctly
passed when using LTO. LTO is a special case of -fembed-bitcode which
it doesn't require embed the bitcode in a special section in the object
file but it requires linker to save that as part of the final executable.

rdar://problem/29274226

Reviewers: mehdi_amini

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D26690

llvm-svn: 287084