swift234

swift -frontend "" shouldn't enter the REPL by default.
This patch fixes a problem where a CompilerInvocation
with no arguments would set the LangaugeOpts etc. up for
the deprecated-integrated-repl, including setting the
module name etc.  Now this only happens if you explicitly
invoke swift -frontend -repl.

Updated testcases that care, and added a new testcase to
ensure that an error is properly generated.

<rdar://problem/17918172>


Swift SVN r21537