Backport LAN (#2131)

backport the old LAN feature to the modern melonDS codebase.

cmake/FindENet.cmake

@@ -0,0 +1,48 @@
+# - Try to find enet
+# Once done this will define
+#
+#  ENET_FOUND - system has enet
+#  ENET_INCLUDE_DIRS - the enet include directory
+#  ENET_LIBRARIES - the libraries needed to use enet
+#
+# $ENETDIR is an environment variable used for finding enet.
+#
+#  Borrowed from The Mana World
+#  http://themanaworld.org/
+#
+# Several changes and additions by Fabian 'x3n' Landau
+# Lots of simplifications by Adrian Friedli
+#                 > www.orxonox.net <
+
+FIND_PATH(ENET_INCLUDE_DIRS enet/enet.h
+    PATHS
+    $ENV{ENETDIR}
+    /usr/local
+    /usr
+    PATH_SUFFIXES include
+)
+
+FIND_LIBRARY(ENET_LIBRARY
+    NAMES enet
+    PATHS
+    $ENV{ENETDIR}
+    /usr/local
+    /usr
+    PATH_SUFFIXES lib
+)
+
+# handle the QUIETLY and REQUIRED arguments and set ENET_FOUND to TRUE if
+# all listed variables are TRUE
+INCLUDE(FindPackageHandleStandardArgs)
+FIND_PACKAGE_HANDLE_STANDARD_ARGS(ENet DEFAULT_MSG ENET_LIBRARY ENET_INCLUDE_DIRS)
+
+IF (ENET_FOUND)
+    IF(WIN32)
+        SET(WINDOWS_ENET_DEPENDENCIES "ws2_32;winmm")
+        SET(ENET_LIBRARIES ${ENET_LIBRARY} ${WINDOWS_ENET_DEPENDENCIES})
+    ELSE(WIN32)
+        SET(ENET_LIBRARIES ${ENET_LIBRARY})
+    ENDIF(WIN32)
+ENDIF (ENET_FOUND)
+
+MARK_AS_ADVANCED(ENET_LIBRARY ENET_LIBRARIES ENET_INCLUDE_DIRS)