Work towards fixing crasher with compound literals...

Before this commit, we crashed in ParseBinOp...

[dylan:~/llvm/tools/clang] admin% ../../Debug/bin/clang -parse-ast-check compound_literal.c
SemaExpr.cpp:1298: failed assertion `(rhs != 0) && "ParseBinOp(): missing right expression"'

With this commit, we still crash in the newly added action ParseCompoundLiteral (which is progress:-)

[dylan:~/llvm/tools/clang] admin% ../../Debug/bin/clang -parse-ast-check compound_literal.c
SemaExpr.cpp:478: failed assertion `(Op != 0) && "ParseCompoundLiteral(): missing expression"'

The crash go away once the actions return AST nodes. I will do this in a separate commit.

llvm-svn: 40032