Renamed and changed the wording of warn_cconv_ignored

As discussed in D64780 the wording of this warning message is being
changed to say 'is not supported' instead of 'ignored', and the
diag ID itself is being changed to warn_cconv_not_supported.

llvm-svn: 366368
diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
index 725a777..ee06f8a 100644
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -4669,7 +4669,7 @@
     break;
 
   case TargetInfo::CCCR_Warning: {
-    Diag(Attrs.getLoc(), diag::warn_cconv_ignored)
+    Diag(Attrs.getLoc(), diag::warn_cconv_unsupported)
         << Attrs << (int)CallingConventionIgnoredReason::ForThisTarget;
 
     // This convention is not valid for the target. Use the default function or