Fix C output and .dockerignore

* Fix the arguments to fidlc for the simple C header, client and server.

* Fix the .dockerignore file. It was using the wrong syntax so it was
  not actually ignoring files, and would upload more than needed.

Change-Id: I75979a72a5dde355699babd40141655747fec526
diff --git a/.dockerignore b/.dockerignore
index f441e61..9baaf96 100644
--- a/.dockerignore
+++ b/.dockerignore
@@ -1,3 +1,3 @@
diff --git a/backend/server.go b/backend/server.go
index ebe02d3..a1ee2f5 100644
--- a/backend/server.go
+++ b/backend/server.go
@@ -405,11 +405,11 @@
 	case C:
 		switch r.Options.File {
 		case "header":
-			return fidlc("--c-header", "/dev/stdout"), nil
+			return fidlc("--fuchsia-only-c-header", "/dev/stdout"), nil
 		case "client":
-			return fidlc("--c-client", "/dev/stdout"), nil
+			return fidlc("--fuchsia-only-c-client", "/dev/stdout"), nil
 		case "server":
-			return fidlc("--c-server", "/dev/stdout"), nil
+			return fidlc("--fuchsia-only-c-server", "/dev/stdout"), nil
 			return internalErrorf("invalid file: %q", r.Options.File)