net/wmwave: fix build with -fno-common

While we are at it:

 - define LICENSE
 - switch to USES=localbase
 - add missing include for errx()

PR:		267588
MFH:		2023Q1
Approved by:	build fix blanket, maintainer timeout
Approved by:	flo (mentor)
Differential Revision: https://reviews.freebsd.org/D38511