feat(asm): add LoongArch encoder with ELF and GOOBJ emission

Assisted-by: DeepSeek V4 Pro

testdata/verify/basic_loong64.s

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+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: BSD-3-Clause
+
+#include "textflag.h"
+
+// add returns a + b.
+TEXT ·add(SB), NOSPLIT, $0-24
+	MOVV	a+0(FP), R4
+	MOVV	b+8(FP), R5
+	ADDV	R5, R4, R4
+	MOVV	R4, ret+16(FP)
+	RET
+
+// arith exercises the 3R integer and FP set.
+TEXT ·arith(SB), NOSPLIT, $0-0
+	ADDV	R4, R5, R6
+	SUBV	R7, R8, R9
+	MULV	R10, R11, R12
+	DIVV	R13, R14, R15
+	AND	R16, R17, R18
+	OR	R18, R19, R20
+	XOR	R20, R21, R2
+	SLLV	R2, R23, R24
+	SRLV	R24, R25, R26
+	SRAV	R26, R27, R28
+	RET
+
+// imm exercises the immediate forms.
+TEXT ·imm(SB), NOSPLIT, $0-0
+	ADDV	$42, R4, R5
+	ADDV	$-8, R6
+	AND	$0xff, R7, R8
+	OR	$1, R9, R10
+	XOR	$0, R11, R12
+	SGT	$100, R13, R14
+	SLLV	$4, R15, R16
+	MOVV	$0x12345, R17
+	RET
+
+// branch exercises conditional and unconditional control flow.
+TEXT ·branch(SB), NOSPLIT, $0-0
+	BEQ	R4, R5, done
+	BNE	R6, R7, skip
+	BLT	R8, R9, done
+	BGE	R10, R11, done
+	BLTU	R12, R13, done
+	BGEU	R14, R15, done
+skip:
+	JMP	loop
+loop:
+	JAL	skip
+	RET
+done:
+	RET

testdata/verify/fp_loong64.s

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+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: BSD-3-Clause
+
+#include "textflag.h"
+
+// fp exercises the floating-point set: 3R arithmetic, 2R unary, compares
+// into FCC, fused multiply-add and the register moves.
+TEXT ·fp(SB), NOSPLIT, $0-0
+	ADDD	F4, F5, F6
+	SUBD	F7, F8, F9
+	MULD	F9, F10, F11
+	DIVD	F11, F12, F13
+	MULF	F13, F14, F15
+	ADDF	F15, F16, F17
+	SQRTD	F17, F18
+	SQRTF	F18, F19
+	ABSD	F19, F20
+	NEGD	F20, F21
+	MOVD	F21, F22
+	CMPEQD	F22, F23, FCC0
+	CMPGTF	F23, F24, FCC1
+	CMPGED	F24, F25, FCC2
+	FMADDD	F0, F1, F2, F3
+	FMSUBF	F3, F4, F5, F6
+	FNMADDD	F6, F7, F8, F9
+	FNMSUBF	F9, F10, F11, F12
+	FMAXD	F12, F13, F14
+	FMINF	F14, F15, F16
+	FMAXAD	F16, F17, F18
+	FMINAF	F18, F19, F20
+	FSCALEBF	F20, F21, F22
+	FCOPYSGD	F22, F23, F24
+	MOVV	F25, R25
+	MOVV	R26, F27
+	MOVW	R28, F29
+	MOVW	F30, R31
+	RET
+
+// mov forms: register moves, immediates (12/32/64-bit), memory with FP/SP
+// pseudo-registers and the register-indexed forms.
+TEXT ·mov(SB), NOSPLIT, $0-16
+	MOVV	R4, R5
+	MOVW	R6, R7
+	MOVB	R8, R9
+	MOVBU	R10, R11
+	MOVHU	R12, R13
+	MOVWU	R14, R15
+	MOVV	$42, R16
+	MOVV	$0x12345, R17
+	MOVV	$0x100000, R18
+	MOVW	$-100, R19
+	MOVV	$0x123456789, R20
+	MOVV	a+0(FP), R21
+	MOVV	R23, b+8(FP)
+	MOVW	c+16(FP), R24
+	MOVV	(R24)(R25), R26
+	MOVV	R27, (R28)(R29)
+	RET
+
+// frame exercises the prologue/epilogue of a function with a real frame.
+TEXT ·frame(SB), NOSPLIT, $32-8
+	MOVV	R4, R5
+	MOVV	arg+0(FP), R6
+	MOVV	R7, local-8(SP)
+	MOVV	local-8(SP), R8
+	MOVV	R9, ret+0(FP)
+	RET
+
+// branches21 exercises the single-register and zero-register branch forms
+// with 21-bit offsets.
+TEXT ·branches21(SB), NOSPLIT, $0-0
+	BEQ	R0, R4, l1
+	BEQ	R5, R0, l2
+	BNE	R0, R6, l3
+	BNE	R7, R0, l4
+	BLTZ	R8, l5
+	BGEZ	R9, l6
+	BLEZ	R10, l7
+	BGTZ	R11, l8
+	JMP	l9
+l1:
+	JMP	l10
+l2:
+	JMP	l11
+l3:
+	JMP	l12
+l4:
+	JMP	l13
+l5:
+	JMP	l14
+l6:
+	JMP	l15
+l7:
+	JMP	l16
+l8:
+	JMP	l16
+l9:
+	MOVV	R1, R2
+l10:
+	LL	(R12), R13
+	LLV	(R14), R15
+	SC	R16, (R17)
+	SCV	R18, (R19)
+	RDTIMED	R20, R21
+	SYSCALL
+	DBAR
+	RET
+l11:
+	JAL	(R30)
+	RET
+l12:
+	BSTRINSV	$7, R4, $0, R5
+	BSTRPICKV	$63, R6, $32, R7
+	ALSLV	$2, R8, R9, R10
+	ADDV16	$65536, R11, R12
+	RET
+l13:
+	MOVV	$0xffffffffffffffff, R13
+	RET
+l14:
+	CPUCFG	R14, R14
+	RET
+l15:
+	NOR	R15, R16, R17
+	ORN	R18, R19, R20
+	ANDN	R21, R24, R25
+	RET
+l16:
+	MOVB	R26, (R27)
+	MOVB	(R28), R29
+	RET
+
+// sbdata loads and stores a static symbol with relocations (the relocation
+// fields are masked before comparison).
+GLOBL	·table(SB), RODATA, $16
+DATA	·table+0(SB)/8, $0x1122334455667788
+DATA	·table+8(SB)/8, $0x8877665544332211
+
+TEXT ·sbdata(SB), NOSPLIT, $0-0
+	MOVV	$·table(SB), R4
+	MOVV	·table(SB), R5
+	MOVV	R6, ·table+8(SB)
+	RET