cmake: treat linker warnings as errors when configuring with SDL_WERROR=ON

cmake/sdlcompilers.cmake

@@ -155,6 +155,18 @@ function(SDL_AddCommonCompilerFlags TARGET)
         endif()
       endif()
     endif()
+
+    if(NOT (APPLE OR MSVC))
+      if(SDL_WERROR)
+        get_property(target_type TARGET ${TARGET} PROPERTY TYPE)
+        if(target_type MATCHES "SHARED_LIBRARY|MODULE_LIBRARY")
+          check_linker_flag(C "-Wl,-fatal-warnings" LINKER_SUPPORTS_WL_FATAL_WARNINGS)
+          if(LINKER_SUPPORTS_WL_FATAL_WARNINGS)
+            target_link_options(${TARGET} PRIVATE "-Wl,-fatal-warnings")
+          endif()
+        endif()
+      endif()
+    endif()
   endif()
 
   if(USE_CLANG)