Seemingly ESP-IDF incorrectly marks RTC FAST memory region
as MALLOC_CAP_EXEC on ESP32-S2 when it isn't. This memory is
the lowest priority, so it only is returned if D/IRAM is exhausted.
Apply this workaround to treat the allocation as failed if it gives us
non-executable RAM back, rather than crashing.
This work was funded through GitHub Sponsors.
Signed-off-by: Angus Gratton <angus@redyak.com.au>
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