Implement parsing of blocks (^{ ... }) in the unwrapped line parser.

Implement parsing of blocks (^{ ... }) in the unwrapped line parser.

This patch makes sure we produce the right number of unwrapped lines,
a follow-up patch will make the whitespace formatting consistent.

Before:
 void f() {
   int i = {[operation setCompletionBlock : ^{ [self onOperationDone];
 }]
 }
 ;
 }

After:
 void f() {
   int i = {[operation setCompletionBlock : ^{
     [self onOperationDone];
   }] };
 }

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@189932 91177308-0d34-0410-b5e6-96231b3b80d8