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

llvm-svn: 298610