druntime vararg implementation

[Mike via Digitalmars-d-learn]

Greetings,

In core.varar. 
(https://github.com/D-Programming-Language/druntime/blob/master/src/core/vararg.d), 
why is the X86 implementation singled out and written in D rather 
than leveraging the standard c library implementation like the 
others?

Mike