rpmalloc-sys fails to build for wasm target on Windows: fatal error: 'unistd.h' file not found

Nobody has claimed this yet.

Not sure if this allocator is intended to also work for wasm, but in my frontend I need speed more than size (it's a UI for a desktop application), so I thought I'd try it..
But it fails to build for wasm:
```
error: failed to run custom build command for `rpmalloc-sys v0.1.3`

--- stdout
TARGET = Some("wasm32-unknown-unknown")
HOST = Some("x86_64-pc-windows-msvc")
CC_wasm32-unknown-unknown = None
CC_wasm32_unknown_unknown = None
TARGET_CC = None
CC = None
CFLAGS_wasm32-unknown-unknown = None
CFLAGS_wasm32_unknown_unknown = None
TARGET_CFLAGS = None
CFLAGS = None
CRATE_CC_NO_DEFAULTS = None
DEBUG = Some("true")
running: "clang" "-O2" "-ffunction-sections" "-fdata-sections" "-fPIC" "-g" "-fno-omit-frame-pointer" "--target=wasm32-unknown-unknown" "-Wall" "-Wextra" "-DENABLE_PRELOAD=1" "-o" "D:\\project\\target\\wasm32-unknown-unknown\\debug\\build\\rpmalloc-sys-21068dcc5b7ecde5\\out\\rpmalloc.o" "-c" "C:\\Users\\me\\.cargo\\registry\\src\\github.com-1ecc6299db9ec823\\rpmalloc-sys-0.1.3\\rpmalloc\\rpmalloc\\rpmalloc.c"
cargo:warning=C:\Users\me\.cargo\registry\src\github.com-1ecc6299db9ec823\rpmalloc-sys-0.1.3\rpmalloc\rpmalloc\rpmalloc.c:122:12: fatal error: 'unistd.h' file not found
cargo:warning=# include
cargo:warning= ^~~~~~~~~~
cargo:warning=1 error generated.
exit code: 1

--- stderr

error occurred: Command "clang" "-O2" "-ffunction-sections" "-fdata-sections" "-fPIC" "-g" "-fno-omit-frame-pointer" "--target=wasm32-unknown-unknown" "-Wall" "-Wextra" "-DENABLE_PRELOAD=1" "-o" "D:\\project\\target\\wasm32-unknown-unknown\\debug\\build\\rpmalloc-sys-21068dcc5b7ecde5\\out\\rpmalloc.o" "-c" "C:\\Users\\me\\.cargo\\registry\\src\\github.com-1ecc6299db9ec823\\rpmalloc-sys-0.1.3\\rpmalloc\\rpmalloc\\rpmalloc.c" with args "clang" did not execute successfully (status code exit code: 1).
```

Reproduce the failure by building rpmalloc-sys v0.1.3 for wasm32-unknown-unknown on Windows, then inspect rpmalloc/rpmalloc/rpmalloc.c around line 122 where unistd.h is included. Determine whether wasm is supported and verify the chosen fix by rerunning the same Cargo build successfully.

Written by the indexing model from the issue text.