Log Message:
libdeflate: update to 1.20.

## Version 1.20

* Improved CRC-32 performance on recent x86 CPUs by adding
  VPCLMULQDQ-accelerated implementations using 256-bit and 512-bit vectors.

* Improved Adler-32 performance on recent x86 CPUs by adding
  VNNI-accelerated implementations using 256-bit and 512-bit vectors.

* Improved CRC-32 and Adler-32 performance on short inputs.

* Optimized the portable implementation of Adler-32.

* Added some basic optimizations for RISC-V.

* Dropped support for gcc versions older than v4.9 (released in 2014)
  and clang versions older than v3.9 (released in 2016).

* Dropped support for CRC-32 acceleration on 32-bit ARM using the ARMv8 pmull or
  crc32 instructions.  This code only worked on CPUs that also have a 64-bit
  mode, and it was already disabled on many compiler versions due to compiler
  limitations.  CRC-32 acceleration remains fully supported on 64-bit ARM.