When we see the a '[' in a postfix expression in Objective-C, perform

a simple, quick check to determine whether the expression starting
with '[' can only be an Objective-C message send. If so, don't parse
it as an array subscript expression. This improves recovery for, e.g.,

  [a method1]
  [a method2]

so that we now produce

  t.m:10:13: error: expected ';' after expression
  [a method]
            ^

instead of some mess about expecting ']'.

llvm-svn: 105221