Enable warn_impcast_literal_float_to_integer by default.

This diagnostic seems to be production ready, it's just an oversight that it
wasn't turned on by default.

The test changes are a bit of a mixed bag. Some tests that seemed like they
clearly didn't need to use this behavior have been modified not to use it.
Others that I couldn't be sure about, I added the necessary expected-warnings
to.

It's possible the diagnostic message could be improved to make it clearer that
this warning can be suppressed by using a value that won't lose precision when
converted to the target type (but can still be a floating point literal, such
as "bool b = 1.0;").

llvm-svn: 154068
diff --git a/clang/test/SemaCXX/overload-call.cpp b/clang/test/SemaCXX/overload-call.cpp
index 1cfe068..b5e1214 100644
--- a/clang/test/SemaCXX/overload-call.cpp
+++ b/clang/test/SemaCXX/overload-call.cpp
@@ -233,7 +233,7 @@
 
 void intref_test() {
   float* ir1 = intref(5);
-  float* ir2 = intref(5.5);
+  float* ir2 = intref(5.5); // expected-warning{{implicit conversion turns literal floating-point number into integer}}
 }
 
 void derived5(C&); // expected-note{{candidate function not viable: cannot bind base class object of type 'A' to derived class reference 'C &' for 1st argument}}