[Flang][OpenMP] Confusing interpretation of threadprivate procedure pointers

## Summary

Flang's interpretation of threadprivate procedure pointers appears to be incorrect. I'd like to illustrate two cases: one that should be accepted and one that should be rejected.

The following are excerpts from language specifications:

* 7.3 `threadprivate` Directive (OpenMP 6.0)

> * The `threadprivate` directive must appear in the declaration section of a scoping unit in which the common block or variable is declared.

> * A variable that appears as an argument in a `threadprivate` directive must be declared in the scope of a module or have the `SAVE` attribute, either explicitly or implicitly.

* 2 Glossary (OpenMP 6.0)

> **variable**
>> A referencing variable or a named data storage block, for which the value can be defined and redefined during the execution of a program; for C/C++, this includes **const**-qualified types when explicitly permitted.

* 15.2.2.4 Procedure pointers (Fortran 2023)

> A procedure pointer is a procedure that has the POINTER attribute.

* 8.5.16 SAVE attribute (Fortran 2023)

> A variable, common block, or procedure pointer declared in the scoping unit of a main program, module, or submodule implicitly has the SAVE attribute, which may be confirmed by explicit specification.

### Should be accepted

OpenMP 6.0 does not specify the order of statements or directives. Therefore, I believe the following code should be accepted.

* test.f90

```fortran
!module mod
!save ::a,b,c,d,e

!$omp threadprivate(a)
external a
pointer a

!$omp threadprivate(b)
pointer b
external b

!$omp threadprivate(c)
procedure(),pointer::c

!$omp threadprivate(d)
procedure()::d
pointer::d

!$omp threadprivate(e)
pointer::e
procedure()::e

external s
end
```

* commands

```console
$ flang --version
flang version 23.0.0git (https://github.com/llvm/llvm-project.git e84e480bb5a53c794f303683df6460ddb44bb7ac)
Target: aarch64-unknown-linux-gnu
Thread model: posix
InstalledDir: /path/to/llvm/build/bin
Build config: +assertions
$ flang test.f90 -fopenmp -c
error: Semantic errors in test.f90
test.f90:4:23: error: 'a' is a data object and may not be EXTERNAL
!$omp threadprivate(a)
^
test.f90:5:12: error: EXTERNAL attribute not allowed on 'a'
external a
^
test.f90:4:23: Declaration of 'a'
!$omp threadprivate(a)
^
test.f90:8:23: error: 'b' is a data object and may not be EXTERNAL
!$omp threadprivate(b)
^
test.f90:10:12: error: EXTERNAL attribute not allowed on 'b'
external b
^
test.f90:8:23: Declaration of 'b'
!$omp threadprivate(b)
^
test.f90:13:24: error: 'c' is already declared as an object
procedure(),pointer::c
^
test.f90:12:23: Declaration of 'c'
!$omp threadprivate(c)
^
test.f90:16:16: error: 'd' is already declared as an object
procedure()::d
^
test.f90:15:23: Declaration of 'd'
!$omp threadprivate(d)
^
test.f90:21:16: error: 'e' is already declared as an object
procedure()::e
^
test.f90:19:23: Declaration of 'e'
!$omp threadprivate(e)
^
```

The issue does not occur under the following conditions:
* Specifying `SAVE` attribute explicitly.
* Placing `threadprivate` directives after the declarations:
```diff
@@ -1,24 +1,24 @@
!module mod
!save ::a,b,c,d,e

- !$omp threadprivate(a)
external a
pointer a
+ !$omp threadprivate(a)

- !$omp threadprivate(b)
pointer b
external b
+ !$omp threadprivate(b)

- !$omp threadprivate(c)
procedure(),pointer::c
+ !$omp threadprivate(c)

- !$omp threadprivate(d)
procedure()::d
pointer::d
+ !$omp threadprivate(d)

- !$omp threadprivate(e)
pointer::e
procedure()::e
+ !$omp threadprivate(e)

external s
end
```

### Should be rejected

Procedure pointers are defined as procedures **with the POINTER attribute**. Without this attribute, these entities are not considered variables. Therefore, I believe the following code should be rejected.

* test2.f90

```fortran
module m
procedure() :: b
!$omp threadprivate(b)

external :: d
!$omp threadprivate(d)

integer,external :: f
!$omp threadprivate(f)
end

program main
procedure() :: bb
!$omp threadprivate(bb)

external :: dd
!$omp threadprivate(dd)

integer,external :: ff
!$omp threadprivate(ff)
end
```

* commands

```console
$ flang --version
flang version 23.0.0git (https://github.com/llvm/llvm-project.git b51054818b78dc395cd4d33f17cfb6e98a36a76d)
Target: aarch64-unknown-linux-gnu
Thread model: posix
InstalledDir: /path/to/llvm/build/bin
Build config: +assertions
$ flang test2.f90 -fopenmp && ./a.out
$
```

## Other Compilers

* GFortran
```console
$ gfortran --version
GNU Fortran (GCC) 15.2.0
Copyright (C) 2025 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ gfortran test.f90 -fopenmp -c
$ gfortran test2.f90 -fopenmp && ./a.out
$
```

* Intel Fortran
```console
$ ifx --version
ifx (IFX) 2025.3.2 20260112
Copyright (C) 1985-2026 Intel Corporation. All rights reserved.

$ ifx -O0 test.f90 -qopenmp -c
test.f90(5): error #6406: Conflicting attributes or multiple declaration of name. [A]
external a
-----------^
test.f90(10): error #6406: Conflicting attributes or multiple declaration of name. [B]
external b
-----------^
test.f90(13): error #6406: Conflicting attributes or multiple declaration of name. [C]
procedure(),pointer::c
-----------------------^
test.f90(16): error #6406: Conflicting attributes or multiple declaration of name. [D]
procedure()::d
---------------^
test.f90(21): error #6406: Conflicting attributes or multiple declaration of name. [E]
procedure()::e
---------------^
test.f90(4): error #7909: A variable that appears in a THREADPRIVATE directive and is not declared in the scope of a module must have the SAVE attribute. [A]
!$omp threadprivate(a)
----------------------^
test.f90(8): error #7909: A variable that appears in a THREADPRIVATE directive and is not declared in the scope of a module must have the SAVE attribute. [B]
!$omp threadprivate(b)
----------------------^
test.f90(12): error #7909: A variable that appears in a THREADPRIVATE directive and is not declared in the scope of a module must have the SAVE attribute. [C]
!$omp threadprivate(c)
----------------------^
test.f90(15): error #7909: A variable that appears in a THREADPRIVATE directive and is not declared in the scope of a module must have the SAVE attribute. [D]
!$omp threadprivate(d)
----------------------^
test.f90(19): error #7909: A variable that appears in a THREADPRIVATE directive and is not declared in the scope of a module must have the SAVE attribute. [E]
!$omp threadprivate(e)
----------------------^
compilation aborted for test.f90 (code 1)
$ ifx -O0 test2.f90 -qopenmp && ./a.out
test2.f90(3): error #6409: This name has already been used as an external procedure name. [B]
!$omp threadprivate(b)
----------------------^
test2.f90(6): error #6409: This name has already been used as an external procedure name. [D]
!$omp threadprivate(d)
----------------------^
test2.f90(9): error #6423: This name has already been used as an external function name. [F]
!$omp threadprivate(f)
----------------------^
test2.f90(9): error #7655: A variable is required in this OpenMP* context. [F]
!$omp threadprivate(f)
----------------------^
test2.f90(14): error #6409: This name has already been used as an external procedure name. [BB]
!$omp threadprivate(bb)
----------------------^
test2.f90(17): error #6409: This name has already been used as an external procedure name. [DD]
!$omp threadprivate(dd)
----------------------^
test2.f90(20): error #6423: This name has already been used as an external function name. [FF]
!$omp threadprivate(ff)
----------------------^
test2.f90(20): error #7655: A variable is required in this OpenMP* context. [FF]
!$omp threadprivate(ff)
----------------------^
compilation aborted for test2.f90 (code 1)
```