[Sema] Issue a warning for integer overflow in struct initializer

Clang wasn't issuing a warning when compiling the following code:

struct s {
  unsigned x;
} s = {
  .x = 4 * 1024 * 1024 * 1024
};

rdar://problem/23399683

Differential Revision: http://reviews.llvm.org/D15097

llvm-svn: 257357
diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index 98c9ceb..4680bcd 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -7853,6 +7853,10 @@
 void Sema::CheckForIntOverflow (Expr *E) {
   if (isa<BinaryOperator>(E->IgnoreParenCasts()))
     E->IgnoreParenCasts()->EvaluateForOverflow(Context);
+  else if (auto InitList = dyn_cast<InitListExpr>(E))
+    for (Expr *E : InitList->inits())
+      if (isa<BinaryOperator>(E->IgnoreParenCasts()))
+        E->IgnoreParenCasts()->EvaluateForOverflow(Context);
 }
 
 namespace {