llvm-nm: Observe -no-llvm-bc for archive members

Summary:
This change fixes the `-no-llvm-bc` flag to work with object files within
archives. Currently the `-no-llvm-bc` flag works for regular object files, but
not static libraries, where it continues to show bitcode symbol info.

Original support was added in D4371.

Reviewers: compnerd, smeenai, pcc

Reviewed By: compnerd

Subscribers: rupprecht, keith, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D48798

llvm-svn: 354196