PANIC on TIM7 IRQ in timer example on armv6-m without FRAME_POINTERS

## Summary
I get consistent crashes while testing apps/examples/timer with disabled CONFIG_FRAME_POINTERS.
With them enabled, it works, but .text consumes +4.5KiB flash.

## Impact
armv6-m thumb MCUs using basic timer peripherals.

## Testing
stm32f072b-disco with custom config, Milandr mdr32f1qi with custom config.

## Details

After porting basic timer functionality from stm32f0l0g0 onto mdr32, I tried to launch some userspace demos. It worked from time to time. It crashed when I tried to reduce consumed flash space. I even enabled tmrinfo debug prints, but they didn't help much in case of crashes -- though they showed successfull signal passing when everything worked.

I think I found a single Kconfig option that breaks it: CONFIG_FRAME_POINTERS=n. It changes CFLAGS from `-fno-omit-frame-pointers -fno-optimize-sibling-calls` to `-fomit-frame-pointers` and saves space. I couldn't get anything else to break at runtime.

Stackdumps/backtraces, defconfigs and workdir patches will follow. I used release/10.3 branch.

Start with apps/examples/timer and compare the configuration and compiler flags with CONFIG_FRAME_POINTERS enabled and disabled. Reproduce the TIM7 IRQ crash on the reported armv6-m boards, then use the promised stackdumps, defconfigs, and workdir patches to identify the failing backtrace or interrupt path; done means the timer example runs reliably without the extra frame-pointer flash cost.

Written by the indexing model from the issue text.