Based on PR pkg/49405
(upstream)
  Update mpg123*  from 1.19.0 to 1.21.0
(pkgsrc)
  Add comment to patch-ad
Tks wiz@ and obache@ for review.x
1.21.0
---
- Use LL as shortcut for LOADLIST remote command, L is taken already (bug 210).
- Less namespace pollution (MPG123_EXPORT in header instead of EXPORT, bug 212).

1.20.1
---
- Make feed reader more efficient when skipping junk by early
  discarding of data from buffers to avoid re-parsing.

1.20.0
---
- Added NEON optimized decoder for AArch64 (ARM 64bit environment)
- enabled for --with-cpu=neon64 (NEON only) or --with-cpu=aarch64
  (runtime switch between neon and generic_fpu, like arm_fpu)
  configuration
- compatible with aarch64-linux-gnu toolchains (from Ubuntu, debian) and Xcode 5
- Added new binary out123 only with the audio output part of mpg123.
  This is a precursor to separating out said code into a simple audio
  output library. It also allows plugging in some processing in a pipe
  before feeding to output.
- Prevent opendir(NULL) for unknown module directory when listing modules.
- some build fixes, among those fixing mpg123-id3dump on Windows

(mef)