Deprecate extern(Pascal) linkage

[ibuclaw]

• D dropped Windows 3.x and 9.x support back in 2.058 - http://dlang.org/deprecate.html#Windows%203.x%20and%20Windows%209x%20support
• It causes problems with ambiguity between extern(Pascal) functions and template value arguments - https://issues.dlang.org/show_bug.cgi?id=14591
• Is not supported by LLVM (http://llvm.org/docs/LangRef.html#calling-conventions) or GCC (https://gcc.gnu.org/onlinedocs/gcc/x86-Function-Attributes.html)

[WalterBright]

Sigh. We need to stop these instant deprecations. There's a process to go through. Documentation - warning - deprecation - error

[yebblies]

Sigh. We need to stop these test-suite failures.

[ibuclaw]

We need to stop these test-suite failures.

The timeouts? Yes...