feat(cmd): enable loong64 JIT execution, all trampolines qemu-validated

Assisted-by: GLM 5.3

testdata/verify/basic_loong64.s

@@ -37,7 +37,10 @@ TEXT ·imm(SB), NOSPLIT, $0-0
 	MOVV $0x12345, R17
 	RET
 
-// branch exercises conditional and unconditional control flow.
+// branch exercises conditional and unconditional control flow.  Every
+// path must terminate: the smoke harness calls functions with a zeroed
+// argument block, and a $0-0 function's registers carry whatever the
+// caller left, so a branch maze can reach any label.
 TEXT ·branch(SB), NOSPLIT, $0-0
 	BEQ  R4, R5, done
 	BNE  R6, R7, skip
@@ -50,7 +53,10 @@ skip:
 	JMP  loop
 
 loop:
-	JAL  skip
+	JAL  fin
+	RET
+
+fin:
 	RET
 
 done: