[llvm] Fix file ignoring inside directories

We have some ! patterns in the .gitignore (for the projects and runtimes
directories), and those patterns end up overriding the previous file
ignores, such that e.g. a .swp file inside the runtimes directory isn't
ignored. Move the file ignores last to ensure they take effect.

Differential Revision: https://reviews.llvm.org/D73253