MAINTAINERS: add LLVM maintainers

Nominate Nathan and myself to be point of contact for clang/LLVM related
support, after a poll at the LLVM BoF at Linux Plumbers Conf 2020.

While corporate sponsorship is beneficial, its important to not entrust
the keys to the nukes with any one entity.  Should Nathan and I find
ourselves at the same employer, I would gladly step down.

Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Sedat Dilek <sedat.dilek@gmail.com>
Acked-by: Nathan Chancellor <natechancellor@gmail.com>
Acked-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Acked-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Acked-by: Masahiro Yamada <masahiroy@kernel.org>
Link: https://lkml.kernel.org/r/20200825143540.2948637-1-ndesaulniers@google.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>