Adding support for mingw-w64 and winpthread

[Vincent R via D.gnu]

Hi,

I would like to generate gdc compiler on msys2/mingw-w64 platform.
The build system on msys2 uses archlinux build architecture and 
the build file is here:
https://github.com/vrichomme/MINGW-packages/blob/newfastrelease/mingw-w64-gcc/PKGBUILD

To generate it I followed the following steps:

1) Install https://msys2.github.io/
2)

$ update-core
$ pacman -Su
$ git clone https://github.com/vrichomme/MINGW-packages.git
$ cd MINGW-packages
$ git fetch origin
$ git checkout -b newfastrelease origin/newfastrelease
$ cd mingw-w64-gcc
$ export MINGW_INSTALLS=mingw64
$ makepkg-mingw -sLf

But of course I get an error because the platform is not 
supported:

/home/Vincent/tmp/MINGW-packages/mingw-w64-gcc/src/build-x86_64-w64-mingw32/./gcc/gdc -B/home/Vincent/tmp/MINGW-packages/mingw-w64-gcc/src/build-x86_64-w64-mingw32/./gcc/ -L/mingw64/x86_64-w64-mingw32/lib -L/mingw64/lib -isystem /mingw64/x86_64-w64-mingw32/include -isystem /mingw64/include -B/mingw64/x86_64-w64-mingw32/bin/ -B/mingw64/x86_64-w64-mingw32/lib/ -isystem /mingw64/x86_64-w64-mingw32/include -isystem /mingw64/x86_64-w64-mingw32/sys-include    -o gcc/gthreads/posix.o -Wall  -g -frelease -O2 -nostdinc -pipe -Wno-deprecated -I ../../../../gcc-5.3.0/libphobos/libdruntime -I ./x86_64-w64-mingw32 -I .  -c ../../../../gcc-5.3.0/libphobos/libdruntime/gcc/gthreads/posix.d
../../../../gcc-5.3.0/libphobos/libdruntime/gcc/gthreads/posix.d:29:1: error: undefined identifier pthread_key_t, did you mean alias gthread_key_t?
  alias gthread_key_t   = pthread_key_t;
  ^
../../../../gcc-5.3.0/libphobos/libdruntime/gcc/gthreads/posix.d:30:1: error: undefined identifier pthread_once_t, did you mean alias gthread_once_t?
  alias gthread_once_t  = pthread_once_t;
  ^
../../../../gcc-5.3.0/libphobos/libdruntime/gcc/gthreads/posix.d:31:1: error: undefined identifier pthread_mutex_t, did you mean alias gthread_mutex_t?
  alias gthread_mutex_t = pthread_mutex_t;
  ^
../../../../gcc-5.3.0/libphobos/libdruntime/gcc/gthreads/posix.d:32:1: error: undefined identifier pthread_mutex_t, did you mean alias gthread_mutex_t?
  alias gthread_recursive_mutex_t = pthread_mutex_t;
  ^
../../../../gcc-5.3.0/libphobos/libdruntime/gcc/gthreads/posix.d:34:27: error: undefined identifier PTHREAD_MUTEX_INITIALIZER
  enum GTHREAD_MUTEX_INIT = PTHREAD_MUTEX_INITIALIZER;
                            ^
../../../../gcc-5.3.0/libphobos/libdruntime/gcc/gthreads/posix.d:35:27: error: undefined identifier PTHREAD_ONCE_INIT, did you mean variable GTHREAD_ONCE_INIT?
  enum GTHREAD_ONCE_INIT  = PTHREAD_ONCE_INIT;
                            ^
../../../../gcc-5.3.0/libphobos/libdruntime/gcc/gthreads/posix.d:36:37: error: undefined identifier PTHREAD_MUTEX_INITIALIZER
  enum GTHREAD_RECURSIVE_MUTEX_INIT = PTHREAD_MUTEX_INITIALIZER;

My question is how does Version is defined when compiling 
core.sys.posix.pthread ?
Because I can see some block corresponding to each platform :

version( linux )
{
...
}
else version( OSX )
{
...
}

But how is defined this value ? Is it based on uname function ?
Can I trace the value of version when compiling the file ?

Thanks