Fix a couple of suboptimalities in error recovery.

1. In the top level of ParseStatementOrDeclaration, don't eat a } if we
   just parsed a statement if it list there.  Also, don't even bother
   emitting an error about a missing semicolon if the statement had a 
   bug (an rbrace is fine).
2. In do/while parsing, don't require a 'while' to be present if the do
   body didn't parse.

This allows us to generate a clean diagnostic for this code:

t.c:1:22: error: expected expression
void foo (void) { do . while (0); }
                     ^

Thanks to Neil for pointing this out.

llvm-svn: 59256