Building in ObjC mode with g++ on Linux

```
--dce full
--library haxe-strings
-m Main
--cpp cpp
-D objc
-D file_extension=mm
```

```

```

This gets me very close, but I get a bunch of parse errors from `ObjcHelpers.h` for some reason?

```
Error: Error while running command
g++ -Iinclude -c -fvisibility=hidden -O2 -fpic -fPIC -Wno-overflow -DHX_LINUX -DHXCPP_M64 -DHXCPP_VISIT_ALLOCS -DHX_SMART_STRINGS -DHXCPP_API_LEVEL=430 -DHXCPP_OBJC -m64 -DHXCPP_M64 -I/usr/share/haxe/lib/hxcpp/4,3,2/include -x objective-c++ -Wno-invalid-offsetof -Wno-format-security -I/usr/include/GNUstep ./src/haxe/IMap.mm -o.../cpp/obj/linux64/f84b96e9_IMap.o

In file included from /usr/share/haxe/lib/hxcpp/4,3,2/include/hxcpp.h:369,
from ./src/haxe/NativeStackTrace.mm:2:
/usr/share/haxe/lib/hxcpp/4,3,2/include/hx/ObjcHelpers.h:14:23: error: expected ‘>’ before ‘*’ token
14 | NSDictionary *_hx_obj_to_nsdictionary(Dynamic d);
| ^
/usr/share/haxe/lib/hxcpp/4,3,2/include/hx/ObjcHelpers.h:14:23: error: cannot find protocol declaration for ‘NSString’
/usr/share/haxe/lib/hxcpp/4,3,2/include/hx/ObjcHelpers.h:14:24: error: expected unqualified-id before ‘,’ token
14 | NSDictionary *_hx_obj_to_nsdictionary(Dynamic d);
| ^
/usr/share/haxe/lib/hxcpp/4,3,2/include/hx/ObjcHelpers.h:14:28: error: expected initializer before ‘>’ token
14 | NSDictionary *_hx_obj_to_nsdictionary(Dynamic d);
| ^
/usr/share/haxe/lib/hxcpp/4,3,2/include/hx/ObjcHelpers.h:19:46: error: cannot find protocol declaration for ‘NSString’
19 | Dynamic _hx_nsdictionary_to_obj(NSDictionary *inDictionary);
| ^~~~~~~~
/usr/share/haxe/lib/hxcpp/4,3,2/include/hx/ObjcHelpers.h:19:46: error: cannot find protocol declaration for ‘NSString’
/usr/share/haxe/lib/hxcpp/4,3,2/include/hx/ObjcHelpers.h:19:45: error: expected primary-expression before ‘<’ token
19 | Dynamic _hx_nsdictionary_to_obj(NSDictionary *inDictionary);
| ^
/usr/share/haxe/lib/hxcpp/4,3,2/include/hx/ObjcHelpers.h:19:55: error: expected primary-expression before ‘*’ token
19 | Dynamic _hx_nsdictionary_to_obj(NSDictionary *inDictionary);
| ^
/usr/share/haxe/lib/hxcpp/4,3,2/include/hx/ObjcHelpers.h:19:56: error: expected primary-expression before ‘,’ token
19 | Dynamic _hx_nsdictionary_to_obj(NSDictionary *inDictionary);
| ^
/usr/share/haxe/lib/hxcpp/4,3,2/include/hx/ObjcHelpers.h:19:60: error: expected primary-expression before ‘>’ token
19 | Dynamic _hx_nsdictionary_to_obj(NSDictionary *inDictionary);
| ^
/usr/share/haxe/lib/hxcpp/4,3,2/include/hx/ObjcHelpers.h:19:63: error: ‘inDictionary’ was not declared in this scope; did you mean ‘NSDictionary’?
19 | Dynamic _hx_nsdictionary_to_obj(NSDictionary *inDictionary);
| ^~~~~~~~~~~~
| NSDictionary
/usr/share/haxe/lib/hxcpp/4,3,2/include/hx/ObjcHelpers.h:33:18: error: expected unqualified-id before ‘^’ token
33 | typedef void (^t)();
| ^
/usr/share/haxe/lib/hxcpp/4,3,2/include/hx/ObjcHelpers.h:33:18: error: expected ‘)’ before ‘^’ token
33 | typedef void (^t)();
| ~^
| )
/usr/share/haxe/lib/hxcpp/4,3,2/include/hx/ObjcHelpers.h:35:11: error: ‘t’ does not name a type; did you mean ‘tm’?
35 | static t create(Dynamic func)
| ^
| tm
```

Any ideas what could be going wrong here? It almost looks like it is not using the objc parser, but it should not include this file unless it is, and also the file doing the inclusion is a `.mm` file and you can see the `-x objective-c++` in the invocation of g++...