Prevent errors in compilation of c++-impl.

Added hidl_array in using statement alongside hidl_vec and hidl_string.

Also added better error messages for the -L flag. I keep on typing
'cpp-impl' instaed of 'c++-impl'.

Bug: 32579492
Test: created vendor implementation for tests.vendor@1.0 and it
compiles.

Change-Id: I2064a8299ff9cada1890f076efd472af39e9c791
diff --git a/main.cpp b/main.cpp
index 29de12c..a4f5dc0 100644
--- a/main.cpp
+++ b/main.cpp
@@ -1171,14 +1171,14 @@
 
             case 'L':
             {
-                CHECK(outputFormat == nullptr); // only one -L option
+                CHECK(outputFormat == nullptr) << "Only one -L option allowed.";
                 for (auto &e : formats) {
                     if (e.mKey == optarg) {
                         outputFormat = &e;
                         break;
                     }
                 }
-                CHECK(outputFormat != nullptr);
+                CHECK(outputFormat != nullptr) << "Output format not recognized.";
                 break;
             }