erofs-utils: lib: switch to on-heap fitblk_buffer for libzstd

 - Allocating VLAs on the stack (or using alloca()) for large sizes
   could exceed the stack limit;

 - It's easier to isolate these buffers on the heap for code sanitizers
   to detect potential bugs.

Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20250703053446.201941-1-hsiangkao@linux.alibaba.com
1 file changed