zig-stm32l476

This is a "bare-metal" Zig project for the NUCLEO-L476RG development board that I'm using to both build up some Zig skills and to tinker with embedded HAL/OS design.

Run zig build to create an ELF file at zig-out/bin/stm32. The upload.sh script creates a hex version of the binary and tries to upload it via OpenOCD.

What's working

Startup: stack, .bss, and .data initialization, minimal vector table (replaced by interrupt.zig)
GPIO
Interrupt handling
SysTick timer