[flang][cuda] Accept variable with UNIFIED attribute in main (#90647)

UNIFIED variables are accept in program scope. Update the check to allow
them.

Author: clementval

flang/lib/Semantics/check-declarations.cpp

@@ -984,7 +984,10 @@ void CheckHelper::CheckObjectEntity(
       }
       break;
     case common::CUDADataAttr::Unified:
-      if ((!subpDetails || inDeviceSubprogram) && !isComponent) {
+      if (((!subpDetails &&
+               symbol.owner().kind() != Scope::Kind::MainProgram) ||
+              inDeviceSubprogram) &&
+          !isComponent) {
         messages_.Say(
             "Object '%s' with ATTRIBUTES(UNIFIED) must be declared in a host subprogram"_err_en_US,
             symbol.name());

flang/test/Semantics/cuf03.cuf

@@ -89,3 +89,7 @@ module m
 
 
 end module
+
+program p
+  real, unified :: um ! ok
+end program