sancov.py: [Py3] Use bytes.decode() explicitly.
sancov.py: [Py3] Use bytes.decode() explicitly.

Or bogus filename like "b'foo'" would be generated.

This is part of https://reviews.llvm.org/D27405

git-svn-id: c199f293c43da69278bea8e88f92242bf3aa95f7@294307 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt