Working in Windows 8.1 and compiling with MinGW

Original code
```xml
<flag value='-DHXCPP_API_LEVEL=${removeQuotes:hxcpp_api_level}' if="hxcpp_api_level" />
```
generate
> haxe cpp.hxml haxelib run hxcpp Build.xml haxe -DHXCPP_M64="1" -DO3="1" -Dhaxe3="1" -Dhaxe_ver ="3.2" -Dhxcpp_api_level= -Dmingw="1" -Dno_shared_libs="1" -I"src/" -I"C:\\ ...

instead 
```xml
<flag value='-DHXCPP_API_LEVEL=${hxcpp_api_level}' if="hxcpp_api_level" />
```
generate
> haxe cpp.hxml haxelib run hxcpp Build.xml haxe -DHXCPP_M64="1" -DO3="1" -Dhaxe3="1" -Dhaxe_ver ="3.2" -Dhxcpp_api_level="312" -Dmingw="1" -Dno_shared_libs="1" -I"src/" -I"C:\\ ...
and it works !!!