[flang] Add one missed semantic check for named constant in common block

[peixin]

Summary

As Fortran 2018 R874, common block object must be one variable name, which
cannot be one named constant. Add this check.

[klausler]

flang/lib/Semantics/resolve-names.cpp

5344

IsNamedConstant is a more readable alternative.

[peixin]

flang/lib/Semantics/resolve-names.cpp

5344

Right. Thanks for the notice. Fixed.

[peixin]

ping @klausler

flang/lib/Semantics/resolve-names.cpp

for (const auto &name : specPartState_.commonBlockObjects) {
     }
     const auto &attrs{symbol->attrs()};
     if (attrs.test(Attr::ALLOCATABLE)) {
       Say(name,
           "ALLOCATABLE object '%s' may not appear in a COMMON block"_err_en_US);
     } else if (attrs.test(Attr::BIND_C)) {
       Say(name,
           "Variable '%s' with BIND attribute may not appear in a COMMON block"_err_en_US);
+    } else if (IsNamedConstant(*symbol)) {
+      Say(name,
+          "A named constant '%s' may not appear in a COMMON block"_err_en_US);
     } else if (IsDummy(*symbol)) {
       Say(name,
           "Dummy argument '%s' may not appear in a COMMON block"_err_en_US);
     } else if (symbol->IsFuncResult()) {
       Say(name,
           "Function result '%s' may not appear in a COMMON block"_err_en_US);
     } else if (const DeclTypeSpec * type{symbol->GetType()}) {
       if (type->category() == DeclTypeSpec::ClassStar) {

flang/test/Semantics/declarations01.f90

 ! RUN: %python %S/test_errors.py %s %flang_fc1
 ! test named constant declarations
 
 function f1() result(x)
   !ERROR: A function result may not also be a named constant
   integer, parameter :: x = 1
-end
 
+  integer, parameter :: x2 = 1
+  integer :: x3
+  !ERROR: A named constant 'x2' may not appear in a COMMON block
+  common /blk/ x2, x3
+
+end