[opt-viewer] Decode HTML bytes for Python 3
Summary:
When using Python 3, `pygments.highlight()` returns a `bytes` object, not
a `str`, causing the call to `str.replace` on the following line to fail
with a runtime exception:
`TypeError: 'str' does not support the buffer interface`. Decode the
bytes into a string in order to fix the exception.
Test Plan:
Run `opt-viewer.py` with Python 3.4, and confirm no runtime error occurs
when calling `str.replace`.
Reviewers: anemet
Reviewed By: anemet
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D36624
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@310741
91177308-0d34-0410-b5e6-
96231b3b80d8