Attempted minimum repro for unwanted stdout in wasm32-wasi builds

This is an attempt at a minimal reproduction to show how wasi_snapshot_preview1.fd_write and friends are sneaking their way into WASM binaries.

This library contains two scenarios between which we can toggle using the NO_PRINTF env var.

• When unset, we use ./lib/repro.c which has a reference to printf in the Print function.
• When set, we use ./lib/repro_no_printf.c which does NOT have a reference to printf.

These two scenarios should ideally NOT have an impact on the final WASM binary because:

1. We're using lto=true
2. The Print function should only get linked in when the print feature is enabled. It is disabled by default.

Usage

Scenario 1: No printf in the c code.

NO_PRINTF=1 cargo build --target=wasm32-wasi --profile=release
wasm-tools print target/wasm32-wasi/release/wasi_import_repro.wasm | grep "(import \| (export"

We can see that there is are absolutely no WASI imports:

  (export "memory" (memory 0))
  (export "fallible_func" (func $fallible_func.command_export))

Here's the baseline binary size:

ls -lah target/wasm32-wasi/release/*.wasm
# -rwxr-xr-x  1 geoff  staff   459B 22 Mar 13:42 target/wasm32-wasi/release/wasi_import_repro.wasm

Scenario 2: A printf call in c code that should be unreferenced.

cargo build --target=wasm32-wasi --profile=release
wasm-tools print target/wasm32-wasi/release/wasi_import_repro.wasm | grep "(import \| (export"

We can see that the fd_* family get pulled along even though they shouldn't have a strong reference.

  (import "wasi_snapshot_preview1" "fd_close" (func $__imported_wasi_snapshot_preview1_fd_close (;0;) (type 2)))
  (import "wasi_snapshot_preview1" "fd_fdstat_get" (func $__imported_wasi_snapshot_preview1_fd_fdstat_get (;1;) (type 3)))
  (import "wasi_snapshot_preview1" "fd_seek" (func $__imported_wasi_snapshot_preview1_fd_seek (;2;) (type 4)))
  (import "wasi_snapshot_preview1" "fd_write" (func $__imported_wasi_snapshot_preview1_fd_write (;3;) (type 5)))
  (export "memory" (memory 0))
  (export "fallible_func" (func $fallible_func.command_export))

We can also see that this has a major impact on the size of the binary:

ls -lah target/wasm32-wasi/release/*.wasm
# -rwxr-xr-x  1 geoff  staff   2.4K 22 Mar 13:34 target/wasm32-wasi/release/wasi_import_repro.wasm