[ODE] __builtin_alloca fix

[Russ Smith]

i've added stuff to the configurator to detect when __builtin_alloca is
necessary under mingw (many people have complained about this but nobody
sent me a patch!). in the process i fix several other makefile problems
with building on mingw. they're fixed now on my environment, but i
know that different flavours of make have several subtle and horrible
issues when building on windows vs unix - primarily in way that commands
get executed (this causes no end of trouble at my work). so anyway,
YMMV.

russ.

-- 
Russell Smith
http://www.q12.org