mpv: small assorted port changes

After aja@ committed my DO_WAF bits from the bigger update diff, here
are the other changes I'd like to get in unrelated to the new version:

* use TLS
* use Python 3
* use SEPARATE_BUILD
- dropping the manual WRKBUILD actually moves it outside WRKSRC

Builds, packages and runs fine on amd64.
Haven't heard from MAINTAINER since a long time.

Feedback? OK?

Index: Makefile
===================================================================
RCS file: /cvs/ports/multimedia/mpv/Makefile,v
retrieving revision 1.44
diff -u -p -r1.44 Makefile
--- Makefile 25 Nov 2018 10:09:25 -0000 1.44
+++ Makefile 9 Dec 2018 23:06:20 -0000
@@ -5,16 +5,16 @@ COMMENT = movie player based on MPlayer
GH_ACCOUNT = mpv-player
GH_PROJECT = mpv
GH_TAGNAME = v0.22.0
-REVISION = 5
+REVISION = 6

CATEGORIES = multimedia x11

-HOMEPAGE = http://mpv.io/
+HOMEPAGE = https://mpv.io/

MAINTAINER = Dmitrij D. Czarkoff <czarkoff@openbsd.org>

WAF = ${WRKSRC}/waf-1.8.19
-MASTER_SITES0 = http://waf.io/
+MASTER_SITES0 = https://waf.io/
DISTFILES = ${DISTNAME}{${GH_TAGNAME}}${EXTRACT_SUFX} ${WAF:T}:0
EXTRACT_ONLY = ${DISTNAME}${EXTRACT_SUFX}

@@ -33,6 +33,8 @@ WANTLIB += xcb-glx z ${MODLUA_WANTLIB}

MODULES = lang/lua \
lang/python
+MODPY_RUNDEP = No
+MODPY_VERSION = ${MODPY_DEFAULT_VERSION_3}

BUILD_DEPENDS = audio/ladspa \
textproc/py-docutils
@@ -49,10 +51,10 @@ LIB_DEPENDS = audio/libcdio \
multimedia/libdvdnav \
multimedia/libv4l

-MODPY_RUNDEP = No
RUN_DEPENDS = devel/desktop-file-utils \
x11/gtk+3,-guic

+SEPARATE_BUILD = Yes
CONFIGURE_ARGS = --confloaddir=${SYSCONFDIR}/mpv \
--confdir=${LOCALBASE}/share/examples/mpv \
--mandir=${LOCALBASE}/man \
@@ -95,8 +97,6 @@ MAKE_ENV += CPPFLAGS="-I${LOCALBASE}/in
MAKE_FLAGS = -o "${WRKBUILD}" -t "${WRKSRC}" --destdir="${DESTDIR}"

NO_TEST = Yes
-
-WRKBUILD = ${WRKSRC}/${MACHINE_ARCH}

.if ${MACHINE_ARCH} == "i386"
CFLAGS += -march=i586