Remove uses of builtin comma operator.

Cleanup for upcoming Clang warning -Wcomma.  No functionality change intended.

llvm-svn: 261270
diff --git a/llvm/lib/Support/APInt.cpp b/llvm/lib/Support/APInt.cpp
index be1b556..83455f6 100644
--- a/llvm/lib/Support/APInt.cpp
+++ b/llvm/lib/Support/APInt.cpp
@@ -2698,8 +2698,10 @@
         break;
       shiftCount--;
       tcShiftRight(srhs, parts, 1);
-      if ((mask >>= 1) == 0)
-        mask = (integerPart) 1 << (integerPartWidth - 1), n--;
+      if ((mask >>= 1) == 0) {
+        mask = (integerPart) 1 << (integerPartWidth - 1);
+        n--;
+      }
   }
 
   return false;