[Tools] Mark output of tools as text if it is text

[Tools] Mark output of tools as text if it is text

Several LLVM tools write text files/streams without using OF_Text.
This can cause problems on platforms which distinguish between
text and binary output. This PR adds the OF_Text flag for the
following tools:

- llvm-dis
- llvm-dwarfdump
- llvm-mca
- llvm-mc (assembler files only)
- opt (assembler files only)
- RemarkStreamer (used e.g. by opt)

Reviewers: rnk, vivekvpandya, Bigcheese, andreadb

Differential Revision: https://reviews.llvm.org/D67696

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@374024 91177308-0d34-0410-b5e6-96231b3b80d8