Make static variables const if possible. Makes them go into a read-only section.

Or fold them into a initializer list which has the same effect. NFC.

llvm-svn: 231598
diff --git a/llvm/lib/CodeGen/InterferenceCache.cpp b/llvm/lib/CodeGen/InterferenceCache.cpp
index 187e015..fd5749b 100644
--- a/llvm/lib/CodeGen/InterferenceCache.cpp
+++ b/llvm/lib/CodeGen/InterferenceCache.cpp
@@ -21,7 +21,8 @@
 #define DEBUG_TYPE "regalloc"
 
 // Static member used for null interference cursors.
-InterferenceCache::BlockInterference InterferenceCache::Cursor::NoInterference;
+const InterferenceCache::BlockInterference
+    InterferenceCache::Cursor::NoInterference;
 
 // Initializes PhysRegEntries (instead of a SmallVector, PhysRegEntries is a
 // buffer of size NumPhysRegs to speed up alloc/clear for targets with large