Log Message:
pv: Update to 1.6.20

Changelog:
1.6.20 - 12 September 2021
  - fix: add missing stddef.h include to number.c (Sam James)

1.6.19 - 5 September 2021
  - fix: starting pv in the background no longer immediately stops unless
    the transfer is to/from the terminal (Andriy Gapon, Jonathan Elchison)
  - fix: using -B, -A, or -T now switches on -C implicitly
    (Johannes Gerer, André Stapf)
  - fix: AIX build fixes (Peter Korsgaard)
  - i18n: updated German "--help" translations (Richard Fonfara)
  - i18n: switched to UTF-8 encoding, added missing translations (de,fr,pt)
  - docs: new "common switches" manual section (Jacek Wielemborek)
  - docs: use placeholder instead of /dev/sda in the manual (Pranav Peshwe)
  - docs: mention MacOS pipes and "-B 1024" in the manual (Jan Venekamp)
  - docs: correct shell in autoconf/scripts/index.sh  (Juan Picca)
  - cleanup: various compiler warnings cleaned up

  Full changelog is below:
  - (r181) added common switches section to manual (Jacek Wielemborek)
  - (r184) use placeholder instead of /dev/sda in the manual (Pranav Peshwe)
  - (r185) replace ash with sh in autoconf/scripts/index.sh (Juan Picca)
  - (r185) added note to manual about "-B 1024" in MacOS pipes (Jan \ 
Venekamp)
  - (r185) fix AIX config check when the CWD contains "yes" (Peter \ 
Korsgaard)
  - (r189) (#1556) updated German "--help" translations (Richard Fonfara)
  - (r189) updated missing German translations and changed to UTF-8 encoding
  - (r191) updated missing French translations and changed to UTF-8 encoding
  - (r193) updated missing Portuguese translations, changed to UTF-8 encoding
  - (r196) (#1563) using -B, -A, or -T now switches on -C implicitly
    (Johannes Gerer, André Stapf)
  - (r199) fixed numerous compiler warnings in newer GCC versions
  - (r200,205) fixed bug where "pv /dev/zero >/dev/null &" stopped
    immediately (Jonathan Elchison, Andriy Gapon)
  - (r203,205) marked unused arguments with GCC unused attribute, started
    using boolean data type for flags, corrected more compiler warnings