Fix warning on Linux

Author: ww898

include/ww898/utf_converters.hpp

@@ -344,7 +344,7 @@ struct conv_strategy<Utf, Outf, It, Oit, true> final
 {
     static void func(It it, It const eit, Oit oit)
     {
-        if (eit - it >= Utf::max_supported_symbol_size)
+        if (static_cast<size_t>(eit - it) >= Utf::max_supported_symbol_size)
         {
             auto const fast_eit = eit - Utf::max_supported_symbol_size;
             while (it < fast_eit)

test/CMakeLists.txt

@@ -32,8 +32,8 @@ if("${CMAKE_CXX_COMPILER_ID}" STREQUAL "MSVC")
 		"$<$<CONFIG:Release>:/Oi>"
 		"$<$<CONFIG:Release>:/Oy->")
 elseif("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU")
-	target_compile_options(utf-cpp-test PRIVATE -std=c++11)
+	target_compile_options(utf-cpp-test PRIVATE -std=c++11 -Wall -Wextra)
 elseif("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang")
-	target_compile_options(utf-cpp-test PRIVATE -std=c++11 -stdlib=libc++)
+	target_compile_options(utf-cpp-test PRIVATE -std=c++11 -stdlib=libc++ -Wall -Wextra)
 	set_target_properties(utf-cpp-test PROPERTIES LINK_FLAGS -stdlib=libc++)
 endif()