LDREX/STREX to Shareable memory needs an external exclusive monitor, and this
Cortex-R5F has none on the path to DDR; Non-shareable uses the core-local
monitor instead. Every atomic compiles to inline LDREX here, since the chip
selects no LIBC_ATOMIC_* backend and falls back to LIBC_ATOMIC_TOOLCHAIN.
Verified on t3-gem-o1: without this the core runs but the console never
appears; with it the same image boots and ostest exits with status 0.
Assisted-by: Claude Code:claude-opus-4-8
Signed-off-by: Ulaş Sertan Kemeç <sertan.usk@gmail.com>
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