Clang Driver: refactor support for writing response files to be specified at Command creation, rather than as part of the Tool.
This resolves the hack I just added to allow Darwin toolchain to vary
its level of support based on -mlinker-version=.
The change preserves the _current_ settings for response-file support.
Some tools look likely to be declaring that they don't support
response files in error, however I kept them as-is in order for this
change to be a simple refactoring.
Differential Revision: https://reviews.llvm.org/D82782