Do not make linker warnings fatal.

Gentoo-bug: 430968

--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -62,8 +62,8 @@
   endif()
 
   if (NOT APPLE)
-    set ( CMAKE_SHARED_LINKER_FLAGS "-Wl,--fatal-warnings -Wl,--no-undefined ${CMAKE_SHARED_LINKER_FLAGS}")
-    set ( CMAKE_MODULE_LINKER_FLAGS "-Wl,--fatal-warnings -Wl,--no-undefined ${CMAKE_MODULE_LINKER_FLAGS}")
+    set ( CMAKE_SHARED_LINKER_FLAGS "-Wl,--no-undefined ${CMAKE_SHARED_LINKER_FLAGS}")
+    set ( CMAKE_MODULE_LINKER_FLAGS "-Wl,--no-undefined ${CMAKE_MODULE_LINKER_FLAGS}")
   endif ()
 
   if (NOT MINGW)