feat(asm): encode indirect JMP and CALL on all four architectures

Assisted-by: GLM 5.3 Flash

testdata/verify/indirect_loong64.s

@@ -0,0 +1,14 @@
+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Indirect control flow: JMP (R4) and JAL (R5) are the toolchain's spellings
+// for jirl; the raw JIRL instruction is deliberately absent, because the Go
+// loong64 assembler deletes it and a parity kernel could not hold it.
+
+#include "textflag.h"
+
+// func f()
+TEXT ·f(SB), NOSPLIT, $0-0
+	JMP (R4)
+	JAL (R5)
+	RET