WasmVM: realloc(ptr, 0) returns non-NULL instead of NULL per POSIX

[NathanFlurry]

Summary

realloc(ptr, 0) returns a non-NULL pointer in WASM (WASI libc / dlmalloc) but returns NULL on native Linux (glibc). POSIX allows either behavior, but the os-test suite expects NULL.

Affected os-test cases

• malloc/realloc-0

Expected behavior

realloc(ptr, 0) should return NULL to match glibc behavior and os-test expectations.

Context

This is a WASI sysroot (dlmalloc) behavioral difference. Discovered via os-test POSIX conformance suite. Tracked in posix-exclusions.json as fail / patched-sysroot.

[NathanFlurry]

Fixed in 5e83691f — realloc(ptr, 0) now returns NULL matching glibc behavior via --wrap=realloc override.