Seems I don't need paths at all. I've installed Code::Blocks 17.12, directed it to the AVR-GCC I already had installed (from past AVR Studio(s)), and added AVRDude for programming. One rub: AVRDude doesn't understand the Jungo USB driver. I found libusb-win32 1.2.6.0, which includes an INF creator and the USB shim driver, which installs easily over the AVRISPMKII I'm using. Huzzah, it talks to chips.
All together, the process is:
- Install Code::Blocks
- Under Compiler settings, select "GNU GCC Compiler for AVR"
- Under Search directories tab, for each sub-tab (Compiler, Linker, Resource compiler), add a path: "E:\Program Files\Atmel\Atmel Toolchain\AVR8 GCC\Native\3.4.1061\avr8-gnu-toolchain\bin" (or wherever it's installed, and whatever version)
- Under Toolchain executables tab, set the installation directory "E:\Program Files\Atmel\Atmel Toolchain\AVR8 GCC\Native\3.4.1061\avr8-gnu-toolchain" (or whatever, again). All the EXE names should be correct by default.
- Make sure the project build settings are correct for your target (namely, compiler flags)
- Add a user-defined tool option (I used the Tools Plus plugin for this). Tool name: "AVRDude - Flash", Command Line: "E:\Program Files\Atmel\Atmel Toolchain\avrdude\avrdude.exe -p $(CPU_CORE) -c AVRISPMKII -U flash:w:$(TARGET_OUTPUT_FILE):e", Output to: Tools window.
Note the use of a user-defined project variable CPU_CORE (e.g. ="m32"). I set this up under Project Build Options, as well as "MCU" (e.g. ="atmega32"), and set the compiler flag with it (Other Compiler Options sub-tab, "-mmcu=$(MCU)" -- do not tick any MCU options on the flags sub-tab). Seems general/useful enough.
Now, to re-familiarize myself with the unseemly details of C...

Tim