Log Message:
musicpd: update to 0.21.4

Now GCC6 is required

Upstream changes:
ver 0.21.4 (2019/01/04)
* database
  - inotify: fix crash bug "terminate called after throwing ..."
  - upnp: implement "list ... group"
* output
  - httpd: declare protocol "HTTP/1.1" instead of "ICY"
* remove libwrap support
* Windows
  - fix "Failed to accept connection: unknown error"
* fix Haiku build