Driver: convert a couple more instances to range based loops

More conversion to range based for loops rather than direct iterators with
dereferencing.  NFC.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@224954 91177308-0d34-0410-b5e6-96231b3b80d8
Fix use-after-destruction introduced in r224924.

getMainExecutable() returns a std::string, assigning its result
to StringRef immediately creates a dangling pointer. This was
detected by half-broken fast-MSan-bootstrap bot.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@224956 91177308-0d34-0410-b5e6-96231b3b80d8
Crash even less on malformed attributes in an incorrect location.

This is a follow-up to r224915.  This adds a bit more line noise to the tests
added in that revision to make sure the parser is ready for a toplevel decl
after each incorrect line.  Use this to move the tests up to where they belong.
This uncovered that the early return was missing a call to
ActOnTagDefinitionError(), so add that. (Also fixes at least one of the crashes
on SLi's bot.)


git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@224958 91177308-0d34-0410-b5e6-96231b3b80d8