Remove use of coverage-file flag

[aaron.ballman]

Summary

The -coverage-file flag was removed in r280306, but I believe this part may have been missed. However, since I'm unfamiliar with this feature, I wanted to be sure.

[aaron.ballman]

Ping. (If I don't hear back, I will assume this is noncontroversial and go ahead and commit sometime next week.)

[aaron.ballman]

I've commit in r301796. Rather than accept my own review and then close it, I am marking it as abandoned.

lib/Driver/Job.cpp

   // arguments.  Therefore, we need to skip the flag and the next argument.
   bool ShouldSkip = llvm::StringSwitch<bool>(Flag)
     .Cases("-MF", "-MT", "-MQ", "-serialize-diagnostic-file", true)
-    .Cases("-o", "-coverage-file", "-dependency-file", true)
+    .Cases("-o", "-dependency-file", true)
     .Cases("-fdebug-compilation-dir", "-diagnostic-log-file", true)
     .Cases("-dwarf-debug-flags", "-ivfsoverlay", true)
     .Default(false);