build: There is no need to check for system libraries on Linux.

CMakeLists.txt

@@ -29,6 +29,7 @@ set(CMAKE_MODULE_PATH
 
 # add definitions
 include(DefineCMakeDefaults)
+include(DefinePlatformDefaults)
 include(DefineCompilerFlags)
 include(DefineInstallationPaths)
 include(DefineOptions.cmake)

ConfigureChecks.cmake

@@ -81,6 +81,7 @@ if (WIN32)
 endif (WIN32)
 
 if (UNIX)
+    if (NOT LINUX)
         # libsocket (Solaris)
         check_library_exists(socket getaddrinfo "" HAVE_LIBSOCKET)
         if (HAVE_LIBSOCKET)
@@ -101,6 +102,7 @@ if (UNIX)
         if (HAVE_LIBRT)
           set(CMAKE_REQUIRED_LIBRARIES ${CMAKE_REQUIRED_LIBRARIES} rt)
         endif (HAVE_LIBRT)
+    endif (NOT LINUX)
 
     check_function_exists(getaddrinfo HAVE_GETADDRINFO)
     check_function_exists(gethostbyname HAVE_GETHOSTBYNAME)