[LowerTypeTests] Skip declarations when determining Thumb support

When looping over all functions in a module to determine whether any of
them is built with support for B.W, we can skip declarations since those
do not have an associated target-feature attribute.
This was found by the assertion from #129600

Reviewed By: statham-arm

Pull Request: #129599

Author: arichardson

llvm/lib/Transforms/IPO/LowerTypeTests.cpp

@@ -1847,6 +1847,9 @@ LowerTypeTestsModule::LowerTypeTestsModule(
     auto &FAM =
         AM.getResult<FunctionAnalysisManagerModuleProxy>(M).getManager();
     for (Function &F : M) {
+      // Skip declarations since we should not query the TTI for them.
+      if (F.isDeclaration())
+        continue;
       auto &TTI = FAM.getResult<TargetIRAnalysis>(F);
       if (TTI.hasArmWideBranch(false))
         CanUseArmJumpTable = true;