Implementing C99 partial re-initialization behavior (DR-253)

Based on previous discussion on the mailing list, clang currently lacks support
for C99 partial re-initialization behavior:
Reference: http://lists.cs.uiuc.edu/pipermail/cfe-dev/2013-April/029188.html
Reference: http://www.open-std.org/jtc1/sc22/wg14/www/docs/dr_253.htm

This patch attempts to fix this problem.

Given the following code snippet,

struct P1 { char x[6]; };
struct LP1 { struct P1 p1; };

struct LP1 l = { .p1 = { "foo" }, .p1.x[2] = 'x' };
// this example is adapted from the example for "struct fred x[]" in DR-253;
// currently clang produces in l: { "\0\0x" },
//   whereas gcc 4.8 produces { "fox" };
// with this fix, clang will also produce: { "fox" };


Differential Review: http://reviews.llvm.org/D5789

llvm-svn: 239446
diff --git a/clang/lib/AST/ExprClassification.cpp b/clang/lib/AST/ExprClassification.cpp
index 5b320c26..9cc612e 100644
--- a/clang/lib/AST/ExprClassification.cpp
+++ b/clang/lib/AST/ExprClassification.cpp
@@ -183,6 +183,8 @@
   case Expr::ObjCIndirectCopyRestoreExprClass:
   case Expr::AtomicExprClass:
   case Expr::CXXFoldExprClass:
+  case Expr::NoInitExprClass:
+  case Expr::DesignatedInitUpdateExprClass:
     return Cl::CL_PRValue;
 
     // Next come the complicated cases.