Add semantic analysis for "blocks". 

Highlights...

- 4 new AST nodes, BlockExpr, BlockStmtExpr, BlockExprExpr, BlockDeclRefExpr.
- Sema::ActOnBlockStart(), ActOnBlockError(), ActOnBlockStmtExpr(), ActOnBlockExprExpr(), ActOnBlockReturnStmt().

Next steps...

- hack Sema::ActOnIdentifierExpr() to deal with block decl refs.
- add attribute handler for byref decls.
- add test cases.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@55710 91177308-0d34-0410-b5e6-96231b3b80d8
10 files changed