Unicorn only builds a x86_64 library, without a x86_64h slice. We can't link against x86_64-only in this manner for static libraries.
Adds a cmake custom target that will build unicorn on first compile and uses this in the build scripts as well. Updates Appveyor and Travis build scripts to work with the new unicorn build, and updates the paths to all of the different artifacts.
This commit also separates clang-format from the linux build, closing #2702.
MerryMage