gerbera: enable matroska and ffmpeg

The latter requires BUILD_PATENTED, as in master.

Backported linking patches for libebml and libmatroska.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

multimedia/gerbera/patches/010-ebml.patch

@@ -0,0 +1,35 @@
+From aab2eacbaad10759294f4fd74bbb5ecef3cf3a8d Mon Sep 17 00:00:00 2001
+From: Fabrice Fontaine <fontaine.fabrice@gmail.com>
+Date: Tue, 24 Dec 2019 22:57:18 +0100
+Subject: [PATCH] cmake/FindMatroska: fix static linking
+
+Fix static linking with libmatrasoka by adding PC_EBM_LIBRARIES to
+EBML_LIBRARIES and PC_MAT_LIBRARIES to MATROSKA_LIBRARIES
+
+Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
+---
+ cmake/FindMatroska.cmake | 4 ++--
+ 1 file changed, 2 insertions(+), 2 deletions(-)
+
+diff --git a/cmake/FindMatroska.cmake b/cmake/FindMatroska.cmake
+index 4b09a5ec..12ca593d 100644
+--- a/cmake/FindMatroska.cmake
++++ b/cmake/FindMatroska.cmake
+@@ -23,7 +23,7 @@ FIND_LIBRARY(EBML_LIBRARY ebml
+ FIND_PACKAGE_HANDLE_STANDARD_ARGS(EBML
+     REQUIRED_VARS EBML_LIBRARY EBML_INCLUDE_DIR)
+ if (EBML_FOUND)
+-    set (EBML_LIBRARIES ${EBML_LIBRARY})
++    set (EBML_LIBRARIES ${EBML_LIBRARY} ${PC_EBM_LIBRARIES})
+     set (EBML_INCLUDE_DIRS ${EBML_INCLUDE_DIR} )
+ endif ()
+ MARK_AS_ADVANCED(
+@@ -41,7 +41,7 @@ find_library(MATROSKA_LIBRARY matroska
+ FIND_PACKAGE_HANDLE_STANDARD_ARGS(MATROSKA
+     REQUIRED_VARS MATROSKA_LIBRARY MATROSKA_INCLUDE_DIR)
+ if (MATROSKA_FOUND)
+-    set (MATROSKA_LIBRARIES ${MATROSKA_LIBRARY})
++    set (MATROSKA_LIBRARIES ${MATROSKA_LIBRARY} ${PC_MAT_LIBRARIES})
+     set (MATROSKA_INCLUDE_DIRS ${MATROSKA_INCLUDE_DIR} )
+ endif ()
+ MARK_AS_ADVANCED(