* rainbow update

* update workflows

* re-add /O2 in nmake Makefile

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

Some finetuning of Github Actions builds

ntru: Match sample_fixed_type to specification

Update NTRU

Oussama Danba caught a bug in how we were handing a test related to
ciphertext encoding. Not a security issue as far as we can tell, but
certainly not the correct behavior.

More detail here: e0ab9525f1

This commit also switches ntruhrss701/avx2/poly_S3_inv to the
Bernstein--Yang code, also slightly simplifies the poly_Rq_to_S3
routine.