Add option to control whether llvm-pdbdump outputs in color

Add option to control whether llvm-pdbdump outputs in color

Adds -color-output option to llvm-pdbdump pretty commands that lets the user
specify whether the output should have color. The default depends on whether
the output is going to a TTY (per prior discussion in
https://reviews.llvm.org/D31246).

This will enable tests that pipe llvm-pdbdump output to FileCheck to work
across platforms without regard to the differences in ANSI codes.

Differential Revision: https://reviews.llvm.org/D31263

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@298610 91177308-0d34-0410-b5e6-96231b3b80d8