Delete Reloc::Default.

Having an enum member named Default is quite confusing: Is it distinct
from the others?

This patch removes that member and instead uses Optional<Reloc> in
places where we have a user input that still hasn't been maped to the
default value, which is now clear has no be one of the remaining 3
options.

llvm-svn: 269988
diff --git a/llvm/lib/LTO/LTOModule.cpp b/llvm/lib/LTO/LTOModule.cpp
index 2ce62a2..7e82677 100644
--- a/llvm/lib/LTO/LTOModule.cpp
+++ b/llvm/lib/LTO/LTOModule.cpp
@@ -230,8 +230,8 @@
       CPU = "cyclone";
   }
 
-  TargetMachine *target = march->createTargetMachine(TripleStr, CPU, FeatureStr,
-                                                     options);
+  TargetMachine *target =
+      march->createTargetMachine(TripleStr, CPU, FeatureStr, options, None);
   M->setDataLayout(target->createDataLayout());
 
   std::unique_ptr<object::IRObjectFile> IRObj(