llgo build -target=wasip1 silently emits a native executable

[cpunion]

Reproducer

On current main (60c30f2ff) on Darwin/arm64:

package main

func main() {
	println("hello")
}

llgo build -target=wasip1 -o hello.wasm hello.go
file hello.wasm

Actual result:

hello.wasm: Mach-O 64-bit executable arm64

The build also prints native libuv/BDWGC dylib warnings, confirming that the named target did not reach the WASI toolchain. The command succeeds, so extension/magic validation is left to the user.

The direct environment path is different but is not a workaround on this revision:

GOOS=wasip1 GOARCH=wasm llgo build -tags=nogc -o hello.wasm hello.go

With LLVM 19 it reaches the WebAssembly backend and crashes while selecting internal/sync.(*HashTrieMap[any,any]).CompareAndDelete; in any case, it is distinct from the named-target bug above.

Expected

-target=wasip1 should either produce a WebAssembly v1 module (\0asm) using the resolved target profile or fail before linking. A post-link target/magic check would also prevent a successful native artifact from being returned for a WebAssembly target.

A small integration test can build the source above with -target=wasip1 and assert the four-byte WebAssembly magic.