The key is to use an object library instead of a static library. The
linker was throwing out the startup code because it's never called.

Fails the same way that cmake does...

These are taken from the verbose output of the existing Makefile (in
blink-openocd).

However it doesn't run...

The configuration step now works, but I haven't told it to use the right
compiler yet.

OUTSET and OUTCLR should use =, not |=. Their purpose is to avoid
read-modify-write operations.

Also there's no reason to make the hello world sketch blink too fast for
the eye to see without waving the board around.