compiler: move wasm ABI workaround to transform package

By considering this as a regular transformation, it can be easily
tested.

transform/wasm-abi_test.go

@@ -0,0 +1,18 @@
+package transform
+
+import (
+	"testing"
+
+	"tinygo.org/x/go-llvm"
+)
+
+func TestWasmABI(t *testing.T) {
+	t.Parallel()
+	testTransform(t, "testdata/wasm-abi", func(mod llvm.Module) {
+		// Run ABI change pass.
+		err := ExternalInt64AsPtr(mod)
+		if err != nil {
+			t.Errorf("failed to change wasm ABI: %v", err)
+		}
+	})
+}