[Flang] Move non-common headers to FortranSupport (llvm#124416)

Move non-common files from FortranCommon to FortranSupport (analogous to
LLVMSupport) such that

* declarations and definitions that are only used by the Flang compiler,
but not by the runtime, are moved to FortranSupport

* declarations and definitions that are used by both ("common"), the
compiler and the runtime, remain in FortranCommon

* generic STL-like/ADT/utility classes and algorithms remain in
FortranCommon

This allows a for cleaner separation between compiler and runtime
components, which are compiled differently. For instance, runtime
sources must not use STL's `<optional>` which causes problems with CUDA
support. Instead, the surrogate header `flang/Common/optional.h` must be
used. This PR fixes this for `fast-int-sel.h`.

Declarations in include/Runtime are also used by both, but are
header-only. `ISO_Fortran_binding_wrapper.h`, a header used by compiler
and runtime, is also moved into FortranCommon.

Author: Meinersbur

flang/include/flang/ISO_Fortran_binding_wrapper.h renamed to flang/include/flang/Common/ISO_Fortran_binding_wrapper.h

@@ -1,14 +1,13 @@
-/*===-- include/flang/ISO_Fortran_binding_wrapper.h ---------------*- C++ -*-===
+/*===-- include/flang/Common/ISO_Fortran_binding_wrapper.h --------*- C++ -*-===
  *
  * 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
  *
- * ===-----------------------------------------------------------------------===
- */
+ *===----------------------------------------------------------------------===*/
 
-#ifndef FORTRAN_ISO_FORTRAN_BINDING_WRAPPER_H_
-#define FORTRAN_ISO_FORTRAN_BINDING_WRAPPER_H_
+#ifndef FORTRAN_COMMON_ISO_FORTRAN_BINDING_WRAPPER_H_
+#define FORTRAN_COMMON_ISO_FORTRAN_BINDING_WRAPPER_H_
 
 /* A thin wrapper around flang/include/ISO_Fortran_binding.h
  * This header file must be included when ISO_Fortran_binding.h
@@ -23,17 +22,17 @@
 
 /* clang-format off */
 #include <stddef.h>
-#include "Common/api-attrs.h"
+#include "api-attrs.h"
 #ifdef __cplusplus
 namespace Fortran {
 namespace ISO {
 #define FORTRAN_ISO_NAMESPACE_ ::Fortran::ISO
 #endif /* __cplusplus */
-#include "ISO_Fortran_binding.h"
+#include "flang/ISO_Fortran_binding.h"
 #ifdef __cplusplus
 } // namespace ISO
 } // namespace Fortran
 #endif /* __cplusplus */
 /* clang-format on */
 
-#endif /* FORTRAN_ISO_FORTRAN_BINDING_WRAPPER_H_ */
+#endif /* FORTRAN_COMMON_ISO_FORTRAN_BINDING_WRAPPER_H_ */

flang/include/flang/Common/erfc-scaled.h

@@ -9,6 +9,9 @@
 #ifndef FORTRAN_COMMON_ERFC_SCALED_H_
 #define FORTRAN_COMMON_ERFC_SCALED_H_
 
+#include <cmath>
+#include <limits>
+
 namespace Fortran::common {
 template <typename T> inline T ErfcScaled(T arg) {
   // Coefficients for approximation to erfc in the first interval.

flang/include/flang/Common/fast-int-set.h

@@ -24,7 +24,7 @@
 #ifndef FORTRAN_COMMON_FAST_INT_SET_H_
 #define FORTRAN_COMMON_FAST_INT_SET_H_
 
-#include <optional>
+#include "optional.h"
 
 namespace Fortran::common {
 
@@ -83,9 +83,9 @@ template <int N> class FastIntSet {
     }
   }
 
-  std::optional<int> PopValue() {
+  optional<int> PopValue() {
     if (IsEmpty()) {
-      return std::nullopt;
+      return nullopt;
     } else {
       return value_[--size_];
     }

flang/include/flang/Common/format.h

@@ -9,8 +9,8 @@
 #ifndef FORTRAN_COMMON_FORMAT_H_
 #define FORTRAN_COMMON_FORMAT_H_
 
+#include "Fortran-consts.h"
 #include "enum-set.h"
-#include "flang/Common/Fortran-consts.h"
 #include <cstring>
 
 // Define a FormatValidator class template to validate a format expression

flang/include/flang/Common/optional.h

@@ -26,7 +26,7 @@
 #ifndef FORTRAN_COMMON_OPTIONAL_H
 #define FORTRAN_COMMON_OPTIONAL_H
 
-#include "flang/Common/api-attrs.h"
+#include "api-attrs.h"
 #include <optional>
 #include <type_traits>
 

flang/include/flang/Common/real.h

@@ -13,7 +13,7 @@
 // The various representations are distinguished by their binary precisions
 // (number of explicit significand bits and any implicit MSB in the fraction).
 
-#include "flang/Common/api-attrs.h"
+#include "api-attrs.h"
 #include <cinttypes>
 
 namespace Fortran::common {

flang/include/flang/Common/reference-wrapper.h

@@ -25,7 +25,7 @@
 #ifndef FORTRAN_COMMON_REFERENCE_WRAPPER_H
 #define FORTRAN_COMMON_REFERENCE_WRAPPER_H
 
-#include "flang/Common/api-attrs.h"
+#include "api-attrs.h"
 #include <functional>
 #include <type_traits>
 

flang/include/flang/Common/restorer.h

@@ -18,8 +18,8 @@
 
 #ifndef FORTRAN_COMMON_RESTORER_H_
 #define FORTRAN_COMMON_RESTORER_H_
+#include "api-attrs.h"
 #include "idioms.h"
-#include "flang/Common/api-attrs.h"
 namespace Fortran::common {
 template <typename A> class Restorer {
 public:

flang/include/flang/Common/target-rounding.h

@@ -9,8 +9,8 @@
 #ifndef FORTRAN_COMMON_TARGET_ROUNDING_H_
 #define FORTRAN_COMMON_TARGET_ROUNDING_H_
 
-#include "flang/Common/Fortran-consts.h"
-#include "flang/Common/enum-set.h"
+#include "Fortran-consts.h"
+#include "enum-set.h"
 
 namespace Fortran::common {
 

flang/include/flang/Common/template.h

@@ -9,8 +9,8 @@
 #ifndef FORTRAN_COMMON_TEMPLATE_H_
 #define FORTRAN_COMMON_TEMPLATE_H_
 
+#include "idioms.h"
 #include "variant.h"
-#include "flang/Common/idioms.h"
 #include <functional>
 #include <optional>
 #include <tuple>