[clang][Interp] Get <=> value info from weak result

This is also what the current interpreter does and a couple of
test cases expect that.

Author: tbaederr

clang/lib/AST/Interp/Interp.h

@@ -808,7 +808,8 @@ bool CMP3(InterpState &S, CodePtr OpPC, const ComparisonCategoryInfo *CmpInfo) {
   }
 
   assert(CmpInfo);
-  const auto *CmpValueInfo = CmpInfo->getValueInfo(CmpResult);
+  const auto *CmpValueInfo =
+      CmpInfo->getValueInfo(CmpInfo->makeWeakResult(CmpResult));
   assert(CmpValueInfo);
   assert(CmpValueInfo->hasValidIntValue());
   const APSInt &IntValue = CmpValueInfo->getIntValue();

clang/test/SemaCXX/compare-modules-cxx2a.cpp

@@ -2,6 +2,7 @@
 // RUN: mkdir -p %t
 
 // RUN: %clang_cc1 -triple x86_64-apple-darwin -fcxx-exceptions -verify -std=c++2a -fmodules -fmodules-cache-path=%t.mcp -I%S/Inputs %s -fno-modules-error-recovery -fmodule-map-file=%S/Inputs/compare.modulemap
+// RUN: %clang_cc1 -triple x86_64-apple-darwin -fcxx-exceptions -verify -std=c++2a -fmodules -fmodules-cache-path=%t.mcp -I%S/Inputs %s -fno-modules-error-recovery -fmodule-map-file=%S/Inputs/compare.modulemap -fexperimental-new-constant-interpreter
 
 struct CC { CC(...); };