The "snag" I found above was a bit worse than I expected.
Of the two ways of declaring some static data in progmem, the one-line version in my last post renders the correct code, but issues a compiler warning.
The typedef version gives no warning, but doesn't actually put any data in progmem. I will try to update the script to get around that. My plan is to find out which warning option that warning is connected to and selectively disable those warnings. -Wuninitialized enabled warnings about uninitialized variables, so -Wno-uninitialized takes them out. Not this particular one though ("only initialized variables can be placed into program memory area").
I also tried disabling everything with -w and then enabling every useful warning one by one. No good. As long as -w is on the command line, it seems all warnings are off even if e.g. -Wunused-variable is also present.
I'll have to peek inside the avr-g++ source code for a hint, and that code is probably hairy...