Don't require iConv; it can be builtin.

CMakeLists.txt

@@ -13,7 +13,7 @@ set(CMAKE_THREAD_PREFER_PTHREAD TRUE)
 find_package(Threads REQUIRED)
 find_package(LibXml2 REQUIRED)
 find_package(ZLIB REQUIRED)
-find_package(iConv REQUIRED)
+find_package(iConv)
 
 list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}")
 include(ExternalProject)