Linker error related to iconv on macOS

[mrexodia]

• cocos2d-x version: latest v4
• devices test on: N/A (applies to mac target only)
• developing environments
  • NDK version: N/A
  • Xcode version: N/A
  • VS version: N/A
  • browser type and version: N/A

Issue description

On OS X Mojave there appears to be an issue related to the iconv library. When creating a project and attempting to build it for mac there is a linker error:

[100%] Linking CXX executable bin/MyGame/MyGame.app/Contents/MacOS/MyGame
Undefined symbols for architecture x86_64:
  "_iconv", referenced from:
      cocos2d::FontAtlas::conversionU32TOGB2312(std::__1::basic_string<char32_t, std::__1::char_traits<char32_t>, std::__1::allocator<char32_t> > const&, std::__1::unordered_map<unsigned int, unsigned int, std::__1::hash<unsigned int>, std::__1::equal_to<unsigned int>, std::__1::allocator<std::__1::pair<unsigned int const, unsigned int> > >&) in libcocos2d.a(CCFontAtlas.cpp.o)
  "_iconv_close", referenced from:
      cocos2d::FontAtlas::~FontAtlas() in libcocos2d.a(CCFontAtlas.cpp.o)
  "_iconv_open", referenced from:
      cocos2d::FontAtlas::conversionU32TOGB2312(std::__1::basic_string<char32_t, std::__1::char_traits<char32_t>, std::__1::allocator<char32_t> > const&, std::__1::unordered_map<unsigned int, unsigned int, std::__1::hash<unsigned int>, std::__1::equal_to<unsigned int>, std::__1::allocator<std::__1::pair<unsigned int const, unsigned int> > >&) in libcocos2d.a(CCFontAtlas.cpp.o)
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make[2]: *** [bin/MyGame/MyGame.app/Contents/MacOS/MyGame] Error 1
make[1]: *** [CMakeFiles/MyGame.dir/all] Error 2
make: *** [all] Error 2

I found the relevant section in CocosConfigDepend.cmake and the issue is that:

find_library(ICONV_LIBRARY iconv)
message(WARNING ${ICONV_LIBRARY})

Will find /usr/local/lib/libiconv.dylib, which does not export those symbols. Changing it to iconv (which should pick up whatever system library) fixes the issue.

It does export the functions, but under a different name:

$ r2 /usr/local/lib/libiconv.dylib
 -- Enable asm.trace to see the tracing information inside the disassembly
[0x00000000]> iE
[Exports]
Num Paddr      Vaddr      Bind     Type Size Name
000 0x000f3230 0x000f3230 GLOBAL   FUNC    0 __libiconv_version
001 0x00003e80 0x00003e80 GLOBAL   FUNC    0 _iconv_canonicalize
002 0x00002f80 0x00002f80 GLOBAL   FUNC    0 _libiconv
003 0x00003010 0x00003010 GLOBAL   FUNC    0 _libiconv_close
004 0x00001000 0x00001000 GLOBAL   FUNC    0 _libiconv_open
005 0x00003040 0x00003040 GLOBAL   FUNC    0 _libiconv_open_into
006 0x00025b70 0x00025b70 GLOBAL   FUNC    0 _libiconv_set_relocation_prefix
007 0x00003860 0x00003860 GLOBAL   FUNC    0 _libiconvctl
008 0x00003aa0 0x00003aa0 GLOBAL   FUNC    0 _libiconvlist