[llvm] Make TargetLowering::getValueType() virtual to fix <N x ptr(7)> crash (PR #126642)

[Matt Arsenault via llvm-commits]

================
@@ -1675,8 +1675,8 @@ class TargetLoweringBase {
   /// operations except for the pointer size.  If AllowUnknown is true, this
   /// will return MVT::Other for types with no EVT counterpart (e.g. structs),
   /// otherwise it will assert.
-  EVT getValueType(const DataLayout &DL, Type *Ty,
-                   bool AllowUnknown = false) const {
+  virtual EVT getValueType(const DataLayout &DL, Type *Ty,
----------------
arsenm wrote:

I'd prefer to directly handle this in getValueType, rather than adding yet another target knob for really low level implementation details. Is this used in any meaningful way? Can we just return an MVT::Other or something in the unhandled case? 

https://github.com/llvm/llvm-project/pull/126642