Improve incompatible triple error

When complaining that the triple is incompatible with all targets, print out the triple not just a generic error about triples not matching.

llvm-svn: 340509
diff --git a/llvm/lib/Support/TargetRegistry.cpp b/llvm/lib/Support/TargetRegistry.cpp
index c5eba57..bb63891 100644
--- a/llvm/lib/Support/TargetRegistry.cpp
+++ b/llvm/lib/Support/TargetRegistry.cpp
@@ -72,7 +72,7 @@
   auto I = find_if(targets(), ArchMatch);
 
   if (I == targets().end()) {
-    Error = "No available targets are compatible with this triple.";
+    Error = "No available targets are compatible with triple \"" + TT + "\"";
     return nullptr;
   }