Make new driver flag '-e' a "Separate" flag instead of "JoinedOrSeparate"

Otherwise it causes conflicts with existing '-e' flags.

Author: artemcm

include/swift/Option/Options.td

@@ -252,7 +252,7 @@ def tools_directory : Separate<["-"], "tools-directory">,
 def D : JoinedOrSeparate<["-"], "D">, Flags<[FrontendOption]>,
   HelpText<"Marks a conditional compilation flag as true">;
 
-def e : JoinedOrSeparate<["-"], "e">, Flags<[NewDriverOnlyOption]>,
+def e : Separate<["-"], "e">, Flags<[NewDriverOnlyOption]>,
   HelpText<"Executes a line of code provided on the command line">;
 
 def F : JoinedOrSeparate<["-"], "F">,