[X86] emitEpilogue - silence implicit integer extension warning.

Silence compiler warning introduced in llvm#125007 - assign the address delta to int64_t, assert it is negative and negate it only as part of the mergeSPAdd call

Fixes llvm#125825

Author: RKSimon

llvm/lib/Target/X86/X86FrameLowering.cpp

@@ -2639,11 +2639,11 @@ void X86FrameLowering::emitEpilogue(MachineFunction &MF,
 
   if (Terminator == MBB.end() || !isTailCallOpcode(Terminator->getOpcode())) {
     // Add the return addr area delta back since we are not tail calling.
-    int64_t Offset = -1 * X86FI->getTCReturnAddrDelta();
-    assert(Offset >= 0 && "TCDelta should never be positive");
-    if (Offset) {
+    int64_t Delta = X86FI->getTCReturnAddrDelta();
+    assert(Delta <= 0 && "TCDelta should never be positive");
+    if (Delta) {
       // Check for possible merge with preceding ADD instruction.
-      Offset = mergeSPAdd(MBB, Terminator, Offset, true);
+      int64_t Offset = mergeSPAdd(MBB, Terminator, -Delta, true);
       emitSPUpdate(MBB, Terminator, DL, Offset, /*InEpilogue=*/true);
     }
   }