[Flang] Add LIT test for NULLIFY statement for procedure pointer.

Author: DanielCChen

flang/lib/Lower/Bridge.cpp

@@ -3099,7 +3099,8 @@ class FirConverter : public Fortran::lower::AbstractConverter {
         Fortran::lower::StatementContext stmtCtx;
         hlfir::Entity pptr = Fortran::lower::convertExprToHLFIR(
             loc, *this, *expr, localSymbols, stmtCtx);
-        auto boxTy{Fortran::lower::getUntypedBoxProcType(&getMLIRContext())};
+        auto boxTy{
+            Fortran::lower::getUntypedBoxProcType(builder->getContext())};
         hlfir::Entity nullBoxProc(
             fir::factory::createNullBoxProc(*builder, loc, boxTy));
         builder->createStoreWithConvert(loc, nullBoxProc, pptr);

flang/test/Lower/HLFIR/procedure-pointer.f90

@@ -106,6 +106,12 @@ subroutine  sub3()
 ! CHECK: %[[VAL_7:.*]] = fir.load %[[VAL_3]]#1 : !fir.ref<!fir.boxproc<(!fir.ref<f32>) -> f32>>
 ! CHECK: %[[VAL_8:.*]] = fir.box_addr %[[VAL_7]] : (!fir.boxproc<(!fir.ref<f32>) -> f32>) -> ((!fir.ref<f32>) -> f32)
 ! CHECK: %[[VAL_9:.*]] = fir.call %[[VAL_8]](%5#1) fastmath<contract> : (!fir.ref<f32>) -> f32
+
+  nullify(p1)
+! CHECK: %[[VAL_10:.*]] = fir.zero_bits () -> ()
+! CHECK: %[[VAL_11:.*]] = fir.emboxproc %[[VAL_10]] : (() -> ()) -> !fir.boxproc<() -> ()>
+! CHECK: %[[VAL_12:.*]] = fir.convert %[[VAL_11]] : (!fir.boxproc<() -> ()>) -> !fir.boxproc<(!fir.ref<f32>) -> f32>
+! CHECK: fir.store %[[VAL_12]] to %[[VAL_3]]#0 : !fir.ref<!fir.boxproc<(!fir.ref<f32>) -> f32>>
 end subroutine
 
 subroutine  sub4()