Compiling fs2 in AIX fails

[ayappanec]

Compiling fs2 in AIX fails with below error.,
rustc --crate-name fs2 /.cargo/registry/src/index.crates.io-d11c229612889eed/fs2-0.4.3/src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --crate-type lib --emit=dep-info,metadata,link -C opt-level=3 -C embed-bitcode=no -C metadata=85c2f526c0211be9 -C extra-filename=-85c2f526c0211be9 --out-dir /tmp/pip-install-2doeq8db/tokenizers_a6dcd574fc864cb793f0985f2a16d7f5/target/release/deps -C strip=debuginfo -L dependency=/tmp/pip-install-2doeq8db/tokenizers_a6dcd574fc864cb793f0985f2a16d7f5/target/release/deps --extern libc=/tmp/pip-install-2doeq8db/tokenizers_a6dcd574fc864cb793f0985f2a16d7f5/target/release/deps/liblibc-3a5102201a3aa852.rmeta --cap-lints allow -C link-arg=-bbigtoc -L/opt/freeware/lib -D_ALL_SOURCE -lpython3.9

error[E0425]: cannot find function `allocate` in module `sys`
   --> /.cargo/registry/src/index.crates.io-d11c229612889eed/fs2-0.4.3/src/lib.rs:104:14
    |
104 |         sys::allocate(self, len)
    |              ^^^^^^^^ not found in `sys`
    |
note: found an item that was configured out
   --> /.cargo/registry/src/index.crates.io-d11c229612889eed/fs2-0.4.3/src/unix.rs:102:8
    |
102 | pub fn allocate(file: &File, len: u64) -> Result<()> {
    |        ^^^^^^^^
note: found an item that was configured out
   --> /.cargo/registry/src/index.crates.io-d11c229612889eed/fs2-0.4.3/src/unix.rs:108:8
    |
108 | pub fn allocate(file: &File, len: u64) -> Result<()> {
    |        ^^^^^^^^
note: found an item that was configured out
   --> /.cargo/registry/src/index.crates.io-d11c229612889eed/fs2-0.4.3/src/unix.rs:143:8
    |
143 | pub fn allocate(file: &File, len: u64) -> Result<()> {
    |        ^^^^^^^^