scudo: Test realloc on increasing size buffers.

While developing a change to the allocator I ended up breaking
realloc on secondary allocations with increasing sizes. That didn't
cause any of the unit tests to fail, which indicated that we're
missing some test coverage here. Add a unit test for that case.

Differential Revision: https://reviews.llvm.org/D102716

GitOrigin-RevId: 8e93d10633d751a3e9169bf9fa68326925ffa097
1 file changed