[flang] Define IEEE_SCALB, IEEE_NEXT_AFTER, IEEE_NEXT_DOWN, IEEE_NEXT_UP

[klausler]

Summary

These functions were missing from the standard intrinsic module
IEEE_ARITHMETIC. IEEE_SCALB is an alias for the standard intrinsic
function SCALE(), and the others are defined as new builtin intrinsic
functions.

flang/lib/Evaluate/fold-real.cpp

return FoldElementalIntrinsic<T, T>(context, std::move(funcRef),
             [](const Scalar<T> &x) -> Scalar<T> { return x.SQRT().value; }));
   } else if (name == "sum") {
     return FoldSum<T>(context, std::move(funcRef));
   } else if (name == "tiny") {
     return Expr<T>{Scalar<T>::TINY()};
   }
   // TODO: dim, dot_product, fraction, matmul,
   // modulo, nearest, norm2, rrspacing, scale,
+  // __builtin_next_after/down/up,
   // set_exponent, spacing, transfer,
   // bessel_jn (transformational) and bessel_yn (transformational)
   return Expr<T>{std::move(funcRef)};
 }
 
 template <int KIND>
 Expr<Type<TypeCategory::Real, KIND>> FoldOperation(
     FoldingContext &context, ComplexComponent<KIND> &&x) {

flang/lib/Evaluate/intrinsics.cpp

// NULL() is a special case handled in Probe() below
             {"pad", SameType, Rank::array, Optionality::optional},
             {"order", AnyInt, Rank::vector, Optionality::optional}},
         SameType, Rank::shaped, IntrinsicClass::transformationalFunction},
     {"rrspacing", {{"x", SameReal}}, SameReal},
     {"same_type_as",
         {{"a", ExtensibleDerived, Rank::anyOrAssumedRank},
             {"b", ExtensibleDerived, Rank::anyOrAssumedRank}},
         DefaultLogical, Rank::scalar, IntrinsicClass::inquiryFunction},
-    {"scale", {{"x", SameReal}, {"i", AnyInt}}, SameReal},
+    {"scale", {{"x", SameReal}, {"i", AnyInt}}, SameReal}, // == IEEE_SCALB()
     {"scan",
         {{"string", SameChar}, {"set", SameChar},
             {"back", AnyLogical, Rank::elemental, Optionality::optional},
             DefaultingKIND},
         KINDInt},
     {"selected_char_kind", {{"name", DefaultChar, Rank::scalar}}, DefaultInt,
         Rank::scalar, IntrinsicClass::transformationalFunction},
     {"selected_int_kind", {{"r", AnyInt, Rank::scalar}}, DefaultInt,
// NULL() is a special case handled in Probe() below
             {"field", SameType, Rank::conformable}},
         SameType, Rank::conformable, IntrinsicClass::transformationalFunction},
     {"verify",
         {{"string", SameChar}, {"set", SameChar},
             {"back", AnyLogical, Rank::elemental, Optionality::optional},
             DefaultingKIND},
         KINDInt},
     {"__builtin_ieee_is_nan", {{"a", AnyFloating}}, DefaultLogical},
+    {"__builtin_ieee_next_after", {{"x", SameReal}, {"y", AnyReal}}, SameReal},
+    {"__builtin_ieee_next_down", {{"x", SameReal}}, SameReal},
+    {"__builtin_ieee_next_up", {{"x", SameReal}}, SameReal},
     {"__builtin_ieee_selected_real_kind", // alias for selected_real_kind
         {{"p", AnyInt, Rank::scalar},
             {"r", AnyInt, Rank::scalar, Optionality::optional},
             {"radix", AnyInt, Rank::scalar, Optionality::optional}},
         DefaultInt, Rank::scalar, IntrinsicClass::transformationalFunction},
     {"__builtin_ieee_support_datatype",
         {{"x", AnyReal, Rank::elemental, Optionality::optional}},
         DefaultLogical},

flang/module/__fortran_builtins.f90

module __Fortran_builtins
 
   type :: __builtin_team_type
     integer(kind=int64) :: __id
   end type
 
   procedure(type(__builtin_c_ptr)) :: __builtin_c_loc
 
   intrinsic :: __builtin_ieee_is_nan
+  intrinsic :: __builtin_ieee_next_after, __builtin_ieee_next_down, &
+    __builtin_ieee_next_up
+  intrinsic :: scale ! for ieee_scalb
   intrinsic :: __builtin_ieee_selected_real_kind
   intrinsic :: __builtin_ieee_support_datatype, &
     __builtin_ieee_support_denormal, __builtin_ieee_support_divide, &
     __builtin_ieee_support_inf, __builtin_ieee_support_io, &
     __builtin_ieee_support_nan, __builtin_ieee_support_sqrt, &
     __builtin_ieee_support_standard, __builtin_ieee_support_subnormal, &
     __builtin_ieee_support_underflow_control
 

flang/module/ieee_arithmetic.f90

 !===-- module/ieee_arithmetic.f90 ------------------------------------------===!
 !
 ! Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 ! See https://llvm.org/LICENSE.txt for license information.
 ! SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 !
 !===------------------------------------------------------------------------===!
 
 ! See Fortran 2018, clause 17.2
 module ieee_arithmetic
 
   use __Fortran_builtins, only: &
     ieee_is_nan => __builtin_ieee_is_nan, &
+    ieee_next_after => __builtin_ieee_next_after, &
+    ieee_next_down => __builtin_ieee_next_down, &
+    ieee_next_up => __builtin_ieee_next_up, &
+    ieee_scalb => scale, &
     ieee_selected_real_kind => __builtin_ieee_selected_real_kind, &
     ieee_support_datatype => __builtin_ieee_support_datatype, &
     ieee_support_denormal => __builtin_ieee_support_denormal, &
     ieee_support_divide => __builtin_ieee_support_divide, &
     ieee_support_inf => __builtin_ieee_support_inf, &
     ieee_support_io => __builtin_ieee_support_io, &
     ieee_support_nan => __builtin_ieee_support_nan, &
     ieee_support_sqrt => __builtin_ieee_support_sqrt, &