Improve wasm32-wasi support

[Starting from 3.41.0 SQLite has wasm32-wasi support out of the
box.][0]

- Set `-DSQLITE_THREADSAFE=0`. Fixes:

```
$ wasmtime target/wasm32-wasi/release/examples/persons.wasm
Error: failed to run main module `target/wasm32-wasi/release/examples/persons.wasm`

Caused by:
    0: failed to instantiate "target/wasm32-wasi/release/examples/persons.wasm"
    1: unknown import: `env::pthread_mutexattr_init` has not been defined
```

- Drop `-DSQLITE_OS_OTHER`. Fixes:

```
$ wasmtime target/wasm32-wasi/release/examples/persons.wasm
Error: failed to run main module `target/wasm32-wasi/release/examples/persons.wasm`

Caused by:
    0: failed to instantiate "target/wasm32-wasi/release/examples/persons.wasm"
    1: unknown import: `env::sqlite3_os_init` has not been defined
```

- [Add wasi specific build flags][1]
- Add basic example
- Also, add instructions how to run it against wasm32-wasi.

Using of file databases is also working, though `--mapdir` arg
should be provided to `wasmtime run`.

[0]: https://wasmlabs.dev/articles/sqlite-wasi-support/
[1]: https://github.com/vmware-labs/webassembly-language-runtimes/blob/main/libs/sqlite/wasi-patches/wlr-build.sh#L11

examples/persons/README.md

@@ -0,0 +1,28 @@
+# Persons example
+
+## Run
+
+```
+$ cargo run --example persons
+```
+
+## Run (wasm32-wasi)
+
+### Requisites
+
+- [wasi-sdk](https://github.com/WebAssembly/wasi-sdk)
+- [wasmtime](https://wasmtime.dev/)
+
+```
+# Set to wasi-sdk directory
+$ export WASI_SDK_PATH=`<wasi-sdk-path>`
+$ export CC_wasm32_wasi="${WASI_SDK_PATH}/bin/clang --sysroot=${WASI_SDK_PATH}/share/wasi-sysroot"
+# Build
+$ cargo build --example persons --target wasm32-wasi --release --features bundled
+# Run
+$ wasmtime target/wasm32-wasi/release/examples/persons.wasm
+Found persons:
+ID: 1, Name: Steven
+ID: 2, Name: John
+ID: 3, Name: Alex
+```