Decide inline truncation for the host when no triple is given

The Node-hosted CLI emits with an empty target triple (the host), while
the native CLI passes its toolchain's triple. Inline truncation keyed on
the triple text alone, so on x86-64 Linux the Node seed emitted
llvm.trunc and the native compiler emitted the inline sequence, and the
native bootstrap's LLVM comparison with the Node seed failed
(self-hosting-native-driver, rebuild-emit). An empty triple now means
the host architecture, as it already does for executable TLS; WASI keeps
the intrinsic. The DataView emission test accepts either truncation
form, since it runs on hosts of both kinds.

packages/compiler/src/backend/llvm/emitter.ts

@@ -811,7 +811,14 @@ export class LlEmitter {
     this.ffiExtendNarrowIntegers =
       options.wasi === true || ffiExtendsNarrowIntegers(options.targetTriple);
     this.wasi = options.wasi === true;
-    this.inlineTrunc = /^(x86_64|amd64)\b/i.test(options.targetTriple ?? "");
+    // An empty triple targets the host, as for executableTls below: the
+    // Node-hosted CLI passes none, the native CLI passes its toolchain's, and
+    // both must emit the same module for the same target.
+    this.inlineTrunc =
+      !this.wasi &&
+      (options.targetTriple
+        ? /^(x86_64|amd64)\b/i.test(options.targetTriple)
+        : process.arch === "x64");
     this.executableTls =
       mod.workers === true &&
       mod.lib === undefined &&

packages/compiler/test/byte-number-emission.test.ts

@@ -45,7 +45,8 @@ test("numeric byte pipelines retain checked fallbacks and use field widths on bo
       expect(wide).toContain("phi i64");
       expect(wide).toContain("@llvm.bswap.i64");
       const offsets = body(ll, "offsets");
-      expect(offsets).toContain("@llvm.trunc.f64");
+      // Truncation is the intrinsic, or inline on an x86-64 host (trunc.ts).
+      expect(offsets).toMatch(/@llvm\.trunc\.f64|@llvm\.copysign\.f64/);
       expect(offsets).toContain("@scr_dataview_set");
       expect(offsets).toContain("@scr_dataview_get");
       expect(offsets).toMatch(/icmp ule i(?:32|64)/);