fix "pc" to be lower case in a target triple, patch by Yonggang Luo


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@79016 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Support/Triple.cpp b/lib/Support/Triple.cpp
index 65af296..71cab39 100644
--- a/lib/Support/Triple.cpp
+++ b/lib/Support/Triple.cpp
@@ -46,7 +46,7 @@
   case UnknownVendor: return "unknown";
 
   case Apple: return "apple";
-  case PC: return "PC";
+  case PC: return "pc";
   }
 
   return "<invalid>";