Poison APFloat::operator==.  Replace existing uses with bitwiseIsEqual.
This means backing out the preceding change to Constants.cpp, alas.

llvm-svn: 41378
diff --git a/llvm/lib/Support/APFloat.cpp b/llvm/lib/Support/APFloat.cpp
index 8f1a566..d2e52ad 100644
--- a/llvm/lib/Support/APFloat.cpp
+++ b/llvm/lib/Support/APFloat.cpp
@@ -276,7 +276,7 @@
 }
 
 bool
-APFloat::operator==(const APFloat &rhs) const {
+APFloat::bitwiseIsEqual(const APFloat &rhs) const {
   if (this == &rhs)
     return true;
   if (semantics != rhs.semantics ||