significantly simplify and clean up error recovery in

ParseObjCPropertyAttribute.  Before, on this code (where
a comma was forgotten):

@property (readonly getter=isAwesome) int _awesome;

we emitted:

crash.m:9:11: error: expected ')'
@property (readonly getter=isAwesome) int _awesome;
          ^
crash.m:9:37: error: type name requires a specifier or qualifier
@property (readonly getter=isAwesome) int _awesome;
                                    ^
crash.m:9:37: error: expected identifier or '('
crash.m:9:37: error: expected ';' at end of declaration list
crash.m:9:1: error: @property requires fields to be named
@property (readonly getter=isAwesome) int _awesome;
^

now we emit:

crash.m:9:21: error: expected ')'
@property (readonly getter=isAwesome) int _awesome;
                    ^
crash.m:9:11: error: to match this '('
@property (readonly getter=isAwesome) int _awesome;
          ^

llvm-svn: 57809