Fix iconv on mac (facebookincubator#208)

The FBX SDK is compiled against a regular libiconv on Windows on Linux (with symbols libconv_open() etc) but on Mac, they compiled it against Apple's modified libiconv, which renames those functions. Annoyingly this means we need to explicitly decline the Conan libiconv package, for that platform only.

Author: zellski

CMakeLists.txt

@@ -50,7 +50,6 @@ find_package(boost_optional MODULE REQUIRED)
 find_package(libxml2 MODULE REQUIRED)
 find_package(zlib MODULE REQUIRED)
 find_package(fmt MODULE REQUIRED)
-find_package(libiconv MODULE REQUIRED)
 
 # create a compilation database for e.g. clang-tidy
 set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
@@ -210,11 +209,18 @@ target_link_libraries(libFBX2glTF
   fmt::fmt
   libxml2::libxml2
   zlib::zlib
-  libiconv::libiconv
   ${CMAKE_DL_LIBS}
   ${CMAKE_THREAD_LIBS_INIT}
 )
 
+if (APPLE)
+ find_package(Iconv MODULE REQUIRED)
+ target_link_libraries(libFBX2glTF Iconv)
+else()
+ find_package(libiconv MODULE REQUIRED)
+ target_link_libraries(libFBX2glTF libiconv::libiconv)
+endif()
+
 target_include_directories(libFBX2glTF PUBLIC
   ${CMAKE_CURRENT_SOURCE_DIR}/src
 )