devel/libsigrokdecode: fix build with python3.9+

- Fix python detection and allow build with python3.9+
- Fix license, add LICENSE_FILE

Approved by:	portmgr blanket

devel/libsigrokdecode/Makefile

@@ -8,13 +8,19 @@ MASTER_SITES=	http://sigrok.org/download/source/libsigrokdecode/
 MAINTAINER=	bsam@FreeBSD.org
 COMMENT=	Framework for hardware logic analyzers, protocol decoders library
 
-LICENSE=	GPLv3
+LICENSE=	GPLv3+
+LICENSE_FILE=	${WRKSRC}/COPYING
 
 GNU_CONFIGURE=	yes
 USES=		gnome libtool pathfix pkgconfig python:3.4+
 USE_GNOME=	glib20
 MAKE_JOBS_UNSAFE=	yes
 USE_LDCONFIG=	yes
 INSTALL_TARGET=	install-strip
+CONFIGURE_ENV= PYTHON3="${PYTHON_CMD}"
+
+post-patch:
+	@${REINPLACE_CMD} -Ee '/python-/ s|3\.[0-9]+|${PYTHON_VER}|g' \
+		${WRKSRC}/configure
 
 .include <bsd.port.mk>