tools: add support for rsvg-convert

TODO: LIBRSVG_USE_RUST should be defined elsewhere, not in librsvg bl3.

Index: defaults.mk
===================================================================
RCS file: /cvsroot/pkgsrc/mk/tools/defaults.mk,v
retrieving revision 1.62
diff -u -p -r1.62 defaults.mk
--- defaults.mk	22 Aug 2018 20:48:37 -0000	1.62
+++ defaults.mk	30 May 2019 17:14:34 -0000
@@ -116,6 +116,7 @@ _TOOLS_VARNAME.pwd=		PWD_CMD
 _TOOLS_VARNAME.rm=		RM
 _TOOLS_VARNAME.rmdir=		RMDIR
 _TOOLS_VARNAME.rpm2pkg=		RPM2PKG
+_TOOLS_VARNAME.rsvg-convert=	RSVG_CONVERT
 _TOOLS_VARNAME.sed=		SED
 _TOOLS_VARNAME.sh=		SH
 _TOOLS_VARNAME.shlock=		SHLOCK
Index: replace.mk
===================================================================
RCS file: /cvsroot/pkgsrc/mk/tools/replace.mk,v
retrieving revision 1.289
diff -u -p -r1.289 replace.mk
--- replace.mk	3 Apr 2019 18:37:24 -0000	1.289
+++ replace.mk	30 May 2019 17:14:35 -0000
@@ -682,6 +682,20 @@ TOOLS_PATH.rpm2pkg=		${LOCALBASE}/sbin/r
 .  endif
 .endif
 
+.if !defined(TOOLS_IGNORE.rsvg-convert) && !empty(_USE_TOOLS:Mrsvg-convert)
+.  if !empty(PKGPATH:Mgraphics/librsvg-c) || !empty(PKGPATH:Mgraphics/librsvg)
+MAKEFLAGS+=			TOOLS_IGNORE.rsvg-convert=
+.  elif !empty(_TOOLS_USE_PKGSRC.rsvg-convert:M[yY][eE][sS])
+.    if ${LIBRSVG_USE_RUST} == "yes"
+TOOLS_DEPENDS.rsvg-convert?=	librsvg-[0-9]*:../../graphics/librsvg
+.    else
+TOOLS_DEPENDS.rsvg-convert?=	librsvg-[0-9]*:../../graphics/librsvg-c
+.    endif
+TOOLS_CREATE+=			rsvg-convert
+TOOLS_PATH.rsvg-convert=	${LOCALBASE}/bin/rsvg-convert
+.  endif
+.endif
+
 .if !defined(TOOLS_IGNORE.sed) && !empty(_USE_TOOLS:Msed)
 .  if !empty(PKGPATH:Mtextproc/nbsed)
 MAKEFLAGS+=			TOOLS_IGNORE.sed=