Apply a forgotten patch to LLVM >3.9

[maleadt]

More specifically, #23611 for making the NVPTX back-end ignore Julia's address spaces.
Tested with LLVM 4.0.1 and 5.0.0

This also adds a .gitattributes file to fully preserve patch contents, because apparently the target file contains CRLF line endings that otherwise get stripped from the patch by git.

cc @iblis17

[iblislin]

good to backport the LLVM 4 part?

[vtjnash]

can we just do * -text to prevent git from ever munging files? (similar to what we suggest at https://github.com/JuliaLang/julia/blob/master/README.windows.md#line-endings)?

[maleadt]

isn't that different? we suggest eol=lf and autocrlf=input, while -text implies no autocrlf at all (potentially introducing crlf line endings)

[davidanthoff]

I think @maleadt is right here. I have another attempt at this in #27291 that might achieve the intended thing, though.

[maleadt]

I don't think there's going to be another 0.6 release.

[maleadt]

I'll just do the conservative thing and merge this as is, with the git attribute only set for patches. We can widen its scope later if we want.
As per @iblis17 request above, I'll add the backport label even though there probably won't be a new 0.6 release anymore.