[flang] Fix crash in semantics on error case (llvm#91482)

An erroneous statement function declaration exposed an unhandled
situation in a utility routine in semantics. Patch that hole and add a
test.

Fixes llvm#91429.

flang/lib/Semantics/tools.cpp

@@ -256,15 +256,17 @@ static const Symbol &FollowHostAssoc(const Symbol &symbol) {
 }
 
 bool IsHostAssociated(const Symbol &symbol, const Scope &scope) {
-  return DoesScopeContain(
-      &GetProgramUnitOrBlockConstructContaining(FollowHostAssoc(symbol)),
-      GetProgramUnitOrBlockConstructContaining(scope));
+  const Symbol &base{FollowHostAssoc(symbol)};
+  return base.owner().IsTopLevel() ||
+      DoesScopeContain(&GetProgramUnitOrBlockConstructContaining(base),
+          GetProgramUnitOrBlockConstructContaining(scope));
 }
 
 bool IsHostAssociatedIntoSubprogram(const Symbol &symbol, const Scope &scope) {
-  return DoesScopeContain(
-      &GetProgramUnitOrBlockConstructContaining(FollowHostAssoc(symbol)),
-      GetProgramUnitContaining(scope));
+  const Symbol &base{FollowHostAssoc(symbol)};
+  return base.owner().IsTopLevel() ||
+      DoesScopeContain(&GetProgramUnitOrBlockConstructContaining(base),
+          GetProgramUnitContaining(scope));
 }
 
 bool IsInStmtFunction(const Symbol &symbol) {

flang/test/Semantics/stmt-func01.f90

@@ -83,3 +83,11 @@ subroutine s4
   !ERROR: VOLATILE attribute may apply only to a variable
   sf(x) = 1.
 end
+
+subroutine s5
+  !ERROR: Invalid specification expression: reference to impure function 'k'
+  real x(k())
+  !WARNING: Name 'k' from host scope should have a type declaration before its local statement function definition
+  !ERROR: 'k' is already declared in this scoping unit
+  k() = 0.0
+end