w3m / boehm-gc issue (really is getcontext in x86_64)

[Markus Pfeiffer <dfly@xxxxxxxxxxxx>]

Dear all,

I started using dragonfly not too long ago. I wanted to build w3m from
pkgsrc on x86_64. Configure failed in a check for libgc, which is installed.
I found out that libgc uses getcontext (and assumes it to exist) which it 
doesn't on x86_64 dragonfly. 
To fix boehm-gc + w3m, I just inserted a defined(__DragonFly__) into mach_deps.c 
Would it be a good idea to port the i386 version of getcontext into x86_64? I 
am willing to do that, then.

Markus