[flang] Exempt construct entities from SAVE check for PURE (llvm#131383)

A PURE subprogram can't have a local variable with the SAVE attribute.
An ASSOCIATE or SELECT TYPE construct entity whose selector is a
variable will return true from IsSave(); exclude them from the local
variable check.

Fixes llvm#131356.

(cherry picked from commit b99dab2)

Author: klausler

flang/lib/Semantics/check-declarations.cpp

@@ -359,7 +359,10 @@ void CheckHelper::Check(const Symbol &symbol) {
       // are not pertinent to the characteristics of the procedure.
       // Restrictions on entities in pure procedure interfaces don't need
       // enforcement.
-    } else if (!FindCommonBlockContaining(symbol) && IsSaved(symbol)) {
+    } else if (symbol.has<AssocEntityDetails>() ||
+        FindCommonBlockContaining(symbol)) {
+      // can look like they have SAVE but are fine in PURE
+    } else if (IsSaved(symbol)) {
       if (IsInitialized(symbol)) {
         messages_.Say(
             "A pure subprogram may not initialize a variable"_err_en_US);

flang/test/Semantics/call10.f90

@@ -36,6 +36,8 @@ pure subroutine s05a
     end subroutine
   end interface
 
+  real :: moduleVar = 1.
+
  contains
 
   subroutine impure(x)
@@ -117,6 +119,8 @@ pure subroutine s05 ! C1589
     !ERROR: A pure subprogram may not initialize a variable
       real :: v6 = 0.
     end block
+    associate (x => moduleVar) ! ok
+    end associate
   end subroutine
   pure subroutine s06 ! C1589
     !ERROR: A pure subprogram may not have a variable with the VOLATILE attribute