CMake: Add libdl and demangle support

cmake/FindDL.cmake

@@ -0,0 +1,20 @@
+include(CheckCXXSourceCompiles)
+set(CMAKE_REQUIRED_LIBRARIES "dl")
+
+check_cxx_source_compiles("
+    #include <dlfcn.h>
+    int main() {
+        Dl_info info;
+        return dladdr(0, &info);
+    }"
+    DL_FOUND
+)
+
+if (DL_FOUND)
+    add_compile_options(
+        -DWITH_DL
+    )
+    link_libraries(dl)
+endif (DL_FOUND)
+
+set(CMAKE_REQUIRED_LIBRARIES "")