Pull Dilithium changes from upstream

Use hash_to_point_ct for both Falcon-512 and 1024

* Update Dilithium

* Alternative montgomery reduce to avoid i386 functest errors

* Explicit casts for msvc

* More casts; bump upstream version; fix metadata

* another cast

* Fix bug in the output of the ct_verify function

A bug in the CCA transformation was reported on the pqc-forum on 2020-12-10
https://groups.google.com/a/list.nist.gov/g/pqc-forum/c/kSUKzDNc5ME

It was fixed today in 669522db63.
This commit ports that fix to PQClean

* add note to SECURITY.md

* update upstream commit in META.yml

Rainbow: Fix out out-of-bounds memset

Disable skipping slow tests

Round 3 Kyber

* rainbow update

* update workflows

* re-add /O2 in nmake Makefile

Makes Kyber-AVX run on MacOS (#251)

Fix missed overflowing mul in FrodoKEM

It happened in another place

Skip overly restrictive clang-tidy checks

my new clang-tidy version comes with some quite restrictive checks that fail on
current code in PQClean.

I have disabled the following three:
https://releases.llvm.org/11.0.0/tools/clang/tools/extra/docs/clang-tidy/checks/llvmlibc-restrict-system-libc-headers.html
https://clang.llvm.org/extra/clang-tidy/checks/cppcoreguidelines-init-variables.html
https://clang.llvm.org/extra/clang-tidy/checks/bugprone-reserved-identifier.html

Fix more overflowing muls in Frodo

hqc-rmrs-256: remove unused static vars

Fix overflowing multiplication in FrodoKEM AES

ntru/poly_rq_mul: explicit casts to satisfy 32-bit clang sanitizer

Disable buggy clang-tidy valist linters

NTRU: faster multiplication for reference implementations

Update Saber and add AVX2 implementation

Add AVX2 Falcon

Round 3 HQC