[docs] Turn of `nasm` highlighting for a code block.

This appears to produce a warning on the docs build bot. It doesn't
reproduce for me, likely because I have a newer (or more full featured)
pygments install.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@338978 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed