PR10101: Recover better from a common copy-paste error: if a function

PR10101: Recover better from a common copy-paste error: if a function
declaration at namespace scope is followed by a semicolon and an open-brace
(or in C++, a 'try', ':' or '='), then the error is probably a function
definition with a spurious ';', rather than a mysterious '{'.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@145372 91177308-0d34-0410-b5e6-96231b3b80d8