DOCFMT is overwritten by d-programming-language.org's makefile
Add external implemented callWithStackShell for Linux/PPC64.

This is required for the garbage collector.
Merge pull request #485 from redstar/ppcthread

Add external implemented callWithStackShell for Linux/PPC64.
Merge pull request #484 from dawgfoto/fix10036

DOCFMT is overwritten by d-programming-language.org's makefile