[APInt] Implement flipAllBitsSlowCase with tcComplement. NFCI

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@299319 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Support/APInt.cpp

@@ -539,8 +539,7 @@ void APInt::clearBit(unsigned bitPosition) {
 
 /// @brief Toggle every bit to its opposite value.
 void APInt::flipAllBitsSlowCase() {
-  for (unsigned i = 0; i < getNumWords(); ++i)
-    pVal[i] ^= UINT64_MAX;
+  tcComplement(pVal, getNumWords());
   clearUnusedBits();
 }