arm64jit: Free up W23 for static alloc.

We shouldn't always reserve W23 for this uncommon case.

Core/MIPS/ARM64/Arm64CompBranch.cpp

@@ -536,7 +536,7 @@ void Arm64Jit::Comp_JumpReg(MIPSOpcode op)
 		delaySlotIsNice = false;
 	CONDITIONAL_NICE_DELAYSLOT;
 
-	ARM64Reg destReg = OTHERTEMPREG;
+	ARM64Reg destReg = INVALID_REG;
 	if (IsSyscall(delaySlotOp)) {
 		gpr.MapReg(rs);
 		MovToPC(gpr.R(rs));  // For syscall to be able to return.
@@ -574,7 +574,9 @@ void Arm64Jit::Comp_JumpReg(MIPSOpcode op)
 		destReg = gpr.R(rs);  // Safe because FlushAll doesn't change any regs
 		FlushAll();
 	} else {
-		// Delay slot - this case is very rare, might be able to free up W24.
+		// Since we can't be in a delay slot, should be safe to steal FLAGTEMPREG for a temp reg.
+		// It will be saved, even if a function is called.
+		destReg = FLAGTEMPREG;
 		gpr.MapReg(rs);
 		MOV(destReg, gpr.R(rs));
 		if (andLink)

Core/MIPS/ARM64/Arm64RegCache.h

@@ -23,8 +23,7 @@
 
 namespace Arm64JitConstants {
 
-const Arm64Gen::ARM64Reg DOWNCOUNTREG = Arm64Gen::W23;
-const Arm64Gen::ARM64Reg OTHERTEMPREG = Arm64Gen::W24;
+const Arm64Gen::ARM64Reg DOWNCOUNTREG = Arm64Gen::W24;
 const Arm64Gen::ARM64Reg FLAGTEMPREG = Arm64Gen::X25;
 const Arm64Gen::ARM64Reg JITBASEREG = Arm64Gen::X26;
 const Arm64Gen::ARM64Reg CTXREG = Arm64Gen::X27;