Basic: Clean up malformed pragma diagnostics

Create a new diagnostic, -Wignored-pragmas and use it to handle any
case where a pragma would have a side effect but is ignored.

llvm-svn: 201102
diff --git a/clang/lib/Parse/ParsePragma.cpp b/clang/lib/Parse/ParsePragma.cpp
index a225c76..41562a4 100644
--- a/clang/lib/Parse/ParsePragma.cpp
+++ b/clang/lib/Parse/ParsePragma.cpp
@@ -530,7 +530,7 @@
     }
 
     // Illegal token!
-    PP.Diag(Tok.getLocation(), diag::warn_pragma_unused_expected_punc);
+    PP.Diag(Tok.getLocation(), diag::warn_pragma_expected_punc) << "unused";
     return;
   }