Add libv4l2 as requirement for the v4l2 plugin.

In order to convert formats not natively supported by obs the
v4l2 userspace library is required. This patch adds a cmake
script to find the library.

cmake/Modules/FindLibv4l2.cmake

@@ -0,0 +1,34 @@
+# Once done these will be defined:
+#
+#  LIBV4L2_FOUND
+#  LIBV4L2_INCLUDE_DIRS
+#  LIBV4L2_LIBRARIES
+#
+
+if(LIBV4L2_INCLUDE_DIRS AND LIBV4L2_LIBRARIES)
+	set(LIBV4L2_FOUND TRUE)
+else()
+	find_package(PkgConfig QUIET)
+	if (PKG_CONFIG_FOUND)
+		pkg_check_modules(_V4L2 QUIET v4l-utils)
+	endif()
+
+	find_path(V4L2_INCLUDE_DIR
+		NAMES libv4l2.h
+		HINTS ${_V4L2_INCLUDE_DIRS} /usr/include /usr/local/include
+			/opt/local/include)
+
+	find_library(V4L2_LIB
+		NAMES v4l2
+		HINTS ${_V4L2_LIBRARY_DIRS} /usr/lib /usr/local/lib
+			/opt/local/lib)
+
+	set(LIBV4L2_INCLUDE_DIRS ${V4L2_INCLUDE_DIR}
+		CACHE PATH "v4l2 include dir")
+	set(LIBV4L2_LIBRARIES "${V4L2_LIB}"
+		CACHE STRING "v4l2 libraries")
+
+	find_package_handle_standard_args(LibV4L2 DEFAULT_MSG V4L2_LIB
+		V4L2_INCLUDE_DIR)
+	mark_as_advanced(V4L2_INCLUDE_DIR V4L2_LIB)
+endif()

plugins/linux-v4l2/CMakeLists.txt

@@ -1,5 +1,13 @@
 include_directories(SYSTEM "${CMAKE_SOURCE_DIR}/libobs")
 
+find_package(Libv4l2)
+if(NOT LIBV4L2_FOUND)
+	message(STATUS "libv4l2 not found, disabling v4l2 plugin")
+	return()
+endif()
+
+include_directories(SYSTEM "${CMAKE_SOURCE_DIR}/libobs")
+
 set(linux-v4l2_SOURCES
 	linux-v4l2.c
 	v4l2-input.c
@@ -10,6 +18,7 @@ add_library(linux-v4l2 MODULE
 )
 target_link_libraries(linux-v4l2
 	libobs
+	${LIBV4L2_LIBRARIES}
 )
 
 install_obs_plugin(linux-v4l2)