[flang] Downgrade benign error message to a warning

It's not conforming to specify the SAVE attribute more than
once for a variable, but it also doesn't hurt anything and
isn't fatal in other Fortran compilers.  Downgrade the
message to a warning for better portability.

Differential Revision: https://reviews.llvm.org/D117153

flang/docs/Extensions.md

@@ -197,6 +197,8 @@ end
 * External unit 0 is predefined and connected to the standard error output,
   and defined as `ERROR_UNIT` in the intrinsic `ISO_FORTRAN_ENV` module.
 * Objects in blank COMMON may be initialized.
+* Multiple specifications of the SAVE attribute on the same object
+  are allowed, with a warning.
 
 ### Extensions supported when enabled by options
 

flang/lib/Semantics/resolve-names.cpp

@@ -4903,7 +4903,7 @@ void DeclarationVisitor::AddSaveName(
     std::set<SourceName> &set, const SourceName &name) {
   auto pair{set.insert(name)};
   if (!pair.second) {
-    Say2(name, "SAVE attribute was already specified on '%s'"_err_en_US,
+    Say2(name, "SAVE attribute was already specified on '%s'"_en_US,
         *pair.first, "Previous specification of SAVE attribute"_en_US);
   }
 }

flang/test/Semantics/resolve107.f90

@@ -0,0 +1,13 @@
+! RUN: %flang_fc1 -fsyntax-only %s 2>&1 | FileCheck %s
+! Check warning on multiple SAVE attribute specifications
+subroutine saves
+  save x
+  save y
+  !CHECK: SAVE attribute was already specified on 'y'
+  integer, save :: y
+  integer, save :: z
+  !CHECK: SAVE attribute was already specified on 'x'
+  !CHECK: SAVE attribute was already specified on 'z'
+  save x,z
+end
+

flang/test/Semantics/resolve45.f90

@@ -53,17 +53,6 @@ subroutine s5
   end block
 end
 
-subroutine s6
-  save x
-  save y
-  !ERROR: SAVE attribute was already specified on 'y'
-  integer, save :: y
-  integer, save :: z
-  !ERROR: SAVE attribute was already specified on 'x'
-  !ERROR: SAVE attribute was already specified on 'z'
-  save x,z
-end
-
 subroutine s7
   !ERROR: 'x' appears as a COMMON block in a SAVE statement but not in a COMMON statement
   save /x/