[NFC] make constructor explicit LiveRange

Without it it can lead to crazy situtation, when passing a LiveRange* to a function expecting a const LiveRange&
the LiveRange* is converted to bool and a new empty LiveRange is created.

Author: Ralender

llvm/include/llvm/CodeGen/LiveInterval.h

@@ -237,9 +237,9 @@ namespace llvm {
     }
 
     /// Constructs a new LiveRange object.
-    LiveRange(bool UseSegmentSet = false)
-        : segmentSet(UseSegmentSet ? std::make_unique<SegmentSet>()
-                                   : nullptr) {}
+    explicit LiveRange(bool UseSegmentSet = false)
+        : segmentSet(UseSegmentSet ? std::make_unique<SegmentSet>() : nullptr) {
+    }
 
     /// Constructs a new LiveRange object by copying segments and valnos from
     /// another LiveRange.