Fix compiler errors on mingw

[tobil4sk]

Currently, there are these building errors with mingw:

D:/Dev/Haxe/hxcpp/src/hx/libs/std/Process.cpp: In function 'Dynamic _hx_std_process_exit(Dynamic, bool)':
D:/Dev/Haxe/hxcpp/src/hx/libs/std/Process.cpp:481:17: error: conversion from 'DWORD' {aka 'long unsigned int'} to 'Dynamic' is ambiguous
  481 |          return rval;
      |                 ^~~~
In file included from D:/Dev/Haxe/hxcpp/include/hxcpp.h:357:
D:/Dev/Haxe/hxcpp/include/Dynamic.h:32:4: note: candidate: 'Dynamic::Dynamic(cpp::UInt64)'
   32 |    Dynamic(cpp::UInt64 inVal);
      |    ^~~~~~~
D:/Dev/Haxe/hxcpp/include/Dynamic.h:31:4: note: candidate: 'Dynamic::Dynamic(cpp::Int64)'
   31 |    Dynamic(cpp::Int64 inVal);
      |    ^~~~~~~
D:/Dev/Haxe/hxcpp/include/Dynamic.h:30:4: note: candidate: 'Dynamic::Dynamic(float)'
   30 |    Dynamic(float inVal);
      |    ^~~~~~~
D:/Dev/Haxe/hxcpp/include/Dynamic.h:29:4: note: candidate: 'Dynamic::Dynamic(double)'
   29 |    Dynamic(double inVal);
      |    ^~~~~~~
D:/Dev/Haxe/hxcpp/include/Dynamic.h:28:4: note: candidate: 'Dynamic::Dynamic(bool)'
   28 |    Dynamic(bool inVal);
      |    ^~~~~~~
D:/Dev/Haxe/hxcpp/include/Dynamic.h:26:4: note: candidate: 'Dynamic::Dynamic(signed char)'
   26 |    Dynamic(signed char inVal);
      |    ^~~~~~~
     D:/Dev/Haxe/hxcpp/include/Dynamic.h:25:4: note: candidate: 'Dynamic::Dynamic(unsigned char)'
   25 |    Dynamic(unsigned char inVal);
      |    ^~~~~~~
D:/Dev/Haxe/hxcpp/include/Dynamic.h:24:4: note: candidate: 'Dynamic::Dynamic(short unsigned int)'
   24 |    Dynamic(unsigned short inVal);
      |    ^~~~~~~
D:/Dev/Haxe/hxcpp/include/Dynamic.h:23:4: note: candidate: 'Dynamic::Dynamic(unsigned int)'
   23 |    Dynamic(unsigned int inVal);
      |    ^~~~~~~
D:/Dev/Haxe/hxcpp/include/Dynamic.h:22:4: note: candidate: 'Dynamic::Dynamic(short int)'
   22 |    Dynamic(short inVal);
      |    ^~~~~~~
D:/Dev/Haxe/hxcpp/include/Dynamic.h:21:4: note: candidate: 'Dynamic::Dynamic(int)'
   21 |    Dynamic(int inVal);
      |    ^~~~~~~
Error: Build failed

Related to d9c02ec

[sebbernery]

Hello ! I had the same issue while compiling lime project with MinGW, thanks for your fix.