feat(riscv64,loong64): operand tail, float DATA and honest port classification

Assisted-by: GLM 5.3 Flash

testdata/verify/branch2_loong64.s

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+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Differential kernel for the loong64 two-operand BEQ/BNE spellings the
+// msan trampolines use: BEQ Rj, target compares against R0 (the beqz form).
+
+#include "textflag.h"
+
+TEXT ·branch2(SB), NOSPLIT, $0-8
+	MOVV arg+0(FP), R4
+	BEQ  R4, zero
+	ADDV $1, R4, R4
+
+zero:
+	MOVV $16, R5
+	BNE  R4, done
+	ADDV $2, R4, R4
+
+done:
+	MOVV R4, ret+0(FP)
+	RET