64-bit DLLs

[Daniel Green]

All tests pass.  However, I see your problem.

In plaindll.d:

version(GNU){ // Workaround for linker error
	void* _tlsstart; // First symbol of the TLS section
	void* _tlsend;
	//int _tls_callbacks_a; // Workaround for GDC/MinGW linker error
}

_tlsstart is the first symbol of the TLS section. _tlsend is the last 
symbol of the TLS section.  Together they are used by D to identify the 
TLS memory region for a given thread.  If they do not come from TLS 
memory then things will not work right.

The MinGW runtime has equivalent symbols __tls_start and __tls_end. 
This is not something likely to change as it's a Windows convention. 
The version of MinGW/GDC you have should define _tlsstart and _tlsend 
symbols automatically if WinMain, DllMain or _Dmain functions exist in 
the current object file.

As of now MinGW/GDC uses alias __tls_start _tlsstart and alias __tls_end 
_tlsend to satisfy those requirements where necessary.

It's the same with _tls_callbacks_a.  Windows convention specifies __xl_a.

The currently posted MinGW64 binaries have an alignment issue with TLS 
memory in 64-bit mode.  It's a segfault that will manifest in the 
garbage collector.

I'll release updated binaries tonight.