[APInt] Remove an unneeded extra temporary APInt from toString.

Turns out udivrem can write its output to the same location as one of its inputs so the extra temporary isn't needed.

llvm-svn: 302772
diff --git a/llvm/lib/Support/APInt.cpp b/llvm/lib/Support/APInt.cpp
index d000ae8..6b01c9b 100644
--- a/llvm/lib/Support/APInt.cpp
+++ b/llvm/lib/Support/APInt.cpp
@@ -1953,15 +1953,11 @@
   } else {
     APInt divisor(Tmp.getBitWidth(), Radix);
     APInt APdigit;
-    APInt tmp2(Tmp.getBitWidth(), 0);
     while (Tmp.getBoolValue()) {
-      udivrem(Tmp, divisor, tmp2, APdigit);
+      udivrem(Tmp, divisor, Tmp, APdigit);
       unsigned Digit = (unsigned)APdigit.getZExtValue();
       assert(Digit < Radix && "divide failed");
       Str.push_back(Digits[Digit]);
-      // Move the quotient into Tmp and move the old allocation of Tmp into
-      // tmp2 to be used on the next loop iteration.
-      std::swap(Tmp, tmp2);
     }
   }