[llvm-cov] Allow specifying distinct architectures for each loaded binary

The coverage tool needs to know which slice to look at when it's handed
a universal binary. Some projects need to look at aggregate coverage
reports for a variety of slices in different binaries: this patch adds
support for these kinds of projects to llvm-cov.

rdar://problem/33579007

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@309747 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed