runtime makefile doesn't properly handle header dependency

[msullivan]

The build system for the runtime doesn't handle dependency on header files. There are common approaches for dealing with this. (Probably the most common approach is "screw it, I'll just use autotools", but there are better ones that that...)

[msullivan]

It looks like the build system tries to make all of the runtime object files depend on all of the header files, using wildcard to get all the .h files in the rt/ directory. This doesn't work, since the wildcard will be expanded in the current directory (that is, the build directory). Instead of trying to fix that, I'm going to do it right way and get the compiler to generate header dependency information.

[msullivan]

The change burned OS X, so I had to back it out.