chromaprint: Fix building on DSM7

[th0ma7]

Motivation: chromaprint fails to build on DSM7, this is an attempt to fix it. Tested over PR #4545
Linked issues:

Checklist

• Build rule all-supported completed successfully
• Package upgrade completed successfully
• New installation of package completed successfully

[th0ma7]

@publicarray Applied over your PR this looks like allowing chromaprint to finally build successfully with DSM7.

[publicarray]

Looks good!

$ fpcalc -version
fpcalc: Relink `/var/packages/chromaprint/target/lib/libpng16.so.16' with `/lib/libpthread.so.0' for IFUNC symbol `longjmp'
fpcalc version 1.5.0 (FFmpeg Lavc58.91.100 Lavf58.45.100 SwR3.7.100)

This relink message is odd, but it still works ok: (x64-7.0). I would be nice to have it fixed, but it's not a stopper.

$ fpcalc -plain /volume1/Media/Music/test.opus 
fpcalc: Relink `/var/packages/chromaprint/target/lib/libpng16.so.16' with `/lib/libpthread.so.0' for IFUNC symbol `longjmp'
AQADtFGqZVKUKAnC4zvuD3-OnzC[...]

I also found this in the logs. This not a bug here, it's in the genetic service scripts. (just here to remind me, @hgy59 or you, if you want to take it)

2021/04/13 08:19:46	===> Step preupgrade. USER=chromaprint GROUP= SHARE_PATH=
2021/04/13 08:19:46	/bin/cp: cannot stat '/volume1/@appstore/chromaprint/var/.': No such file or directory

[th0ma7]

Closing, now merged part of #4545