Branch: slice/S.8b. Commit only there; never to trunk.

Read first:

• docs/phases/S-small-targets.md: S.2 runs on Zephyr's emulated qemu_cortex_m0 board, which is QEMU's microbit machine (an nRF51 with a Cortex-M0). S.8c runs emitted Thumb code on the same machine.
• qemu/PIN.md, qemu/inventory.yml, src/glint/qemu/minikconf.cr and src/glint/qemu/build/compile.cr: how Glint builds qemu-system-aarch64 without Meson, from a static inventory.
• spec/qemu/minikconf_spec.cr and spec/qemu_inventory_spec.cr: the cross-checks that say which sources a device selection needs.

These facts were checked in QEMU 11.1.2's source:

• hw/arm/Kconfig line 680: config MICROBIT, depends on TCG && ARM, select NRF51_SOC; NRF51_SOC selects ARM_V7M, I2C and UNIMP. target/arm/Kconfig: AARCH64 selects ARM, and ARM selects ARM_COMPATIBLE_SEMIHOSTING under TCG. So qemu-system-aarch64 can carry the machine; no qemu-system-arm is needed.
• The inventory already has the ARM_V7M sources (hw/arm/armv7m.c, hw/intc/armv7m_nvic.c, hw/timer/armv7m_systick.c, hw/misc/armv7m_ras.c).
• hw/arm/nrf51_soc.c: flash at 0x0, SRAM at 0x20000000, CPU cortex-m0. hw/arm/microbit.c loads -kernel with armv7m_load_kernel, which takes an ELF or else a raw image at 0.
• target/arm/tcg/m_helper.c line 2375: on M-profile, BKPT 0xab is a semihosting call when semihosting is on. semihosting/arm-compat-semi.c: SYS_EXIT_EXTENDED (0x20) with a block {0x20026, code} exits QEMU with code.

Claim. Glint's qemu-system-aarch64 also runs QEMU's microbit machine, so Cortex-M0 code can be run and checked on x86-1 with the QEMU Glint builds.

Passage. S.8's demonstration: emitted code is "run on qemu_cortex_m0".

Make:

• CONFIG_MICROBIT=y in the aarch64 device selection (Minikconf::ARM_VIRT_MAK, or a sibling constant both the build and the spec read; keep one place).
• The sources and generated inputs the cross-check specs then ask for, added to qemu/inventory.yml with their Meson source sets, and qemu/PIN.md's counts updated.
• spec/qemu/microbit_spec.cr, pending without GLINT_QEMU_AARCH64 (or the build's default path) like the other QEMU specs. It writes a raw image of a few hand-encoded Thumb instructions: a vector table (initial SP 0x20004000, reset handler with the Thumb bit), then SYS_EXIT_EXTENDED through BKPT 0xab with exit code 7. It runs qemu-system-aarch64 -M microbit -kernel IMAGE -semihosting-config enable=on,target=native -display none -monitor none -serial none with a timeout, and expects exit status 7. It also checks that -M help lists microbit.

Demonstration. bin/glint-qemu aarch64 rebuilds; the minikconf and inventory specs pass with QEMU_SRC set; the new spec passes; and bin/glint-run aarch64 is not affected (it can't build aarch64 images on x86-1 yet, so say so rather than claim it). Report the binary's size before and after.

Constraints. Only the sources the selection needs. No change to the x86_64 binary. crystal tool format --check passes.