wasm: Fix unreachable paths

When the last instruction is a debug instruction, the type of it is void.
Similarly for 'noreturn' emit an 'unreachable' instruction to tell the wasm-validator
the path cannot be reached.

Also respect the '--strip' flag in the self-hosted wasm linker and not emit a 'name' section
when the flag is set to `true`.

src/arch/wasm/CodeGen.zig

@@ -871,7 +871,8 @@ fn genFunc(self: *Self) InnerError!void {
     // we emit an unreachable instruction to tell the stack validator that part will never be reached.
     if (func_type.returns.len != 0 and self.air.instructions.len > 0) {
         const inst = @intCast(u32, self.air.instructions.len - 1);
-        if (self.air.typeOfIndex(inst).isNoReturn()) {
+        const last_inst_ty = self.air.typeOfIndex(inst);
+        if (!last_inst_ty.hasRuntimeBitsIgnoreComptime() or last_inst_ty.isNoReturn()) {
             try self.addTag(.@"unreachable");
         }
     }

src/link/Wasm.zig

@@ -1897,7 +1897,7 @@ pub fn flushModule(self: *Wasm, comp: *Compilation, prog_node: *std.Progress.Nod
         if (data_section_index) |data_index| {
             try self.emitDataRelocations(file, arena, data_index, symbol_table);
         }
-    } else {
+    } else if (!self.base.options.strip) {
         try self.emitNameSection(file, arena);
     }
 }