Investigate and fix heap allocation test failure with GNU Arm Embedded Toolchain 10.3-2021.07

[LDong-Arm]

No description provided.

[LDong-Arm]

There's a bug in newlib-nano 4.1.0:

The commit 84d0689 "Nano-malloc: Fix for unwanted external heap fragmentation" from newlib 4.1.0 introduced several optimizations, one of which is as follows:

When the last chunk in the free list is smaller than requested, nano_malloc() calls srbk(0) to see if the heap's current head is adjacent to this chunk, and if so it asks srbk() for the difference in bytes only and expands the current chunk.

This doesn't work if the heap consists of non-contiguous regions. srbk(0) returns the the current region's head if the latter has any remaining capacity. But if this capacity is not enough for the second (non-trivial) call to srbk() described above, allocation will happen from the next region if available. Expanding the current chunk won't work and will result in a segmentation fault.