This is the first commit in a series that will reformat
all the python files in the LLVM repository.

Reformatting is done with `black`.

See more information here:

https://discourse.llvm.org/t/rfc-document-and-standardize-python-code-style

Reviewed By: jhenderson, JDevlieghere, MatzeB

Differential Revision: https://reviews.llvm.org/D150545

This updates llvm/utils/sysroot.py to include the "DIA SDK" folder in the
sysroot.

It also updates the build to look for the DIA SDK there if a sysroot is set.

This requires moving LLVM_WINSYSROOT to config-ix.cmake.

For the GN build, I chose to pass a qualified path to diaguids in libs instead
of pushing a config with a `/libpath:` flag. The former requires a GN with
https://gn-review.googlesource.com/c/gn/+/12200, the latter requires D109624.
The former is more like the cmake build, arguably a bit simpler, and it's
easier to check for the wrong GN revision and easier to update GN.

Differential Revision: https://reviews.llvm.org/D109708

This is a tiny bit messy because compiler-rt needs different sysroots for
macOS, iOS, etc. We want sysroot.py to create something that is a hermetic
representation of all build deps, so it needs to create a directory that
contains all needed SDKs, and these subdirectories are then passed to
cmake which passes each of these _subdirectories_ as different -isysroot
flags while building the runtime libraries.

Differential Revision: https://reviews.llvm.org/D96958

CMAKE_SYSROOT works fine here, and `sysroot.py make-fake`
borders on trivial here, but I suppose it's still nice
to have a consistent script to set these up across platforms.

And these are the platforms where we can do real sysroot management one
day.

Differential Revision: https://reviews.llvm.org/D96882

Also add a script for sysroot management. For now, it can only create
fake sysroots that just symlink to local folders. This is useful for
testing.

Differential Revision: https://reviews.llvm.org/D96868