[NFC] SCEVExpander: add SetCurrentDebugLocation() / getCurrentDebugLocation() wrappers

[lebedev.ri]

Summary

The internal Builder is private, which means there is
currently no way to set the debuginfo locations for SCEVExpander.
This only adds the wrappers, but does not use them anywhere.

[lebedev.ri]

Rebased, NFC.

[sanjoy]

Lgtm

[lebedev.ri]

In D61007#1644130, @sanjoy wrote:

Lgtm

I was not landing this as-is because i don't have an use-case for this until D61144.

llvm/trunk/include/llvm/Analysis/ScalarEvolutionExpander.h

#endif
     /// insert point is not a block terminator).
     void setInsertPoint(Instruction *IP) {
       assert(IP);
       Builder.SetInsertPoint(IP);
     }
 
     /// Clear the current insertion point. This is useful if the instruction
     /// that had been serving as the insertion point may have been deleted.
-    void clearInsertPoint() {
-      Builder.ClearInsertionPoint();
+    void clearInsertPoint() { Builder.ClearInsertionPoint(); }
+
+    /// Set location information used by debugging information.
+    void SetCurrentDebugLocation(DebugLoc L) {
+      Builder.SetCurrentDebugLocation(std::move(L));
+    }
+
+    /// Get location information used by debugging information.
+    const DebugLoc &getCurrentDebugLocation() const {
+      return Builder.getCurrentDebugLocation();
     }
 
     /// Return true if the specified instruction was inserted by the code
     /// rewriter.  If so, the client should not modify the instruction.
     bool isInsertedInstruction(Instruction *I) const {
       return InsertedValues.count(I) || InsertedPostIncValues.count(I);
     }