Fix bogus assertion using getSExtValue for legitimate values, like -1 in

an 128-bit-wide integer.  No testcase; the issue I ran into depends on 
local changes.

llvm-svn: 60311

include/llvm/ADT/APInt.h

@@ -1046,7 +1046,7 @@ public:
     if (isSingleWord())
       return int64_t(VAL << (APINT_BITS_PER_WORD - BitWidth)) >> 
                      (APINT_BITS_PER_WORD - BitWidth);
-    assert(getActiveBits() <= 64 && "Too many bits for int64_t");
+    assert(getMinSignedBits() <= 64 && "Too many bits for int64_t");
     return int64_t(pVal[0]);
   }