Describe the bug
sbrk is an old function deprecated and removed from grass many times, but there is a leftover in r.terraflow (https://github.com/OSGeo/grass/blob/master/raster/r.terraflow/stats.cpp#L130 and https://github.com/OSGeo/grass/blob/master/raster/r.terraflow/stats.cpp#L154)

To Reproduce

Expected behavior
Remove sbrk in favor of mmap?

Screenshots
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System description (please complete the following information):

• Operating System: FreeBSD aarch64/riscv64 and MacOS
• GRASS GIS version All

Additional context
Add any other context about the problem here.