Latent 32-bit make check warnings

[embg]

We have some latent mingw gcc 32-bit make check warnings (when compiling with -Wall):

In function 'BIT_getLowerBits',
    inlined from 'BIT_addBits' at ../lib/compress/../common/bitstream.h:184:27,
    inlined from 'ZSTD_encodeSequences_body' at ../lib/compress/zstd_compress_sequences.c:316:5,
    inlined from 'ZSTD_encodeSequences_default' at ../lib/compress/zstd_compress_sequences.c:392:12,
    inlined from 'ZSTD_encodeSequences' at ../lib/compress/zstd_compress_sequences.c:437:12:
../lib/compress/../common/bitstream.h:171:35: warning: array subscript 32 is above array bounds of 'const unsigned int[32]' [-Warray-bounds]
  171 |     return bitContainer & BIT_mask[nbBits];
      |                           ~~~~~~~~^~~~~~~~

These warnings existed in dev at least three weeks ago (see the logs on this job). It's hard to bisect this because I don't have an msys2 setup locally, and very old CI job logs are not in retention any more. Opening an issue to track this because it might be release-blocking.

[embg]

Discussed with @terrelln, the warnings are bogus.