DebugInfo: Classify noreturn function types as non-reconstructible

This information isn't preserved in the DWARF description of function
types (though probably should be - it's preserved on the function
declarations/definitions themselves through the DW_AT_noreturn attribute
- but we should move or also include that in the subroutine type itself
too - but for now, with it not being there, the DWARF is lossy and
can't be reconstructed)

clang/lib/CodeGen/CGDebugInfo.cpp

@@ -5078,6 +5078,7 @@ struct ReconstitutableType : public RecursiveASTVisitor<ReconstitutableType> {
   bool VisitFunctionProtoType(FunctionProtoType *FT) {
     // noexcept is not encoded in DWARF, so the reversi
     Reconstitutable &= !isNoexceptExceptionSpec(FT->getExceptionSpecType());
+    Reconstitutable &= !FT->getNoReturnAttr();
     return Reconstitutable;
   }
   bool VisitRecordType(RecordType *RT) {

clang/test/CodeGenCXX/debug-info-simple-template-names.cpp

@@ -116,4 +116,10 @@ void f() {
 
   f1<const unsigned _BitInt(5)>();
   // CHECK: !DISubprogram(name: "f1<const unsigned _BitInt(5)>",
+
+  // Add a parameter just so this differs from other attributed function types
+  // that don't mangle differently.
+  int fnrt() __attribute__((noreturn));
+  f1<decltype(fnrt)>();
+  // CHECK: !DISubprogram(name: "f1<int () __attribute__((noreturn))>",
 }

cross-project-tests/debuginfo-tests/clang_llvm_roundtrip/simplified_template_names.cpp

@@ -325,6 +325,8 @@ int main() {
   f1<int t1<>::*>();
   void fcc() __attribute__((swiftcall));
   f1<decltype(fcc)>();
+  int fnrt() __attribute__((noreturn));
+  f1<decltype(fnrt)>();
 }
 void t8::mem() {
   struct t7 { };