[flang] Change C889 from error into warning

This constraint is used in OMP2012 benchmark, and other compilers do not
enforce it. Change it into one warning. This addresses the issue
llvm/llvm-project#56003.

Reviewed By: klausler, kiranchandramohan

Differential Revision: https://reviews.llvm.org/D127740

Author: PeixinQiao

flang/lib/Semantics/resolve-names.cpp

@@ -5251,7 +5251,7 @@ void DeclarationVisitor::CheckSaveStmts() {
     } else if (specPartState_.saveInfo.saveAll) {
       // C889 - note that pgi, ifort, xlf do not enforce this constraint
       Say2(name,
-          "Explicit SAVE of '%s' is redundant due to global SAVE statement"_err_en_US,
+          "Explicit SAVE of '%s' is redundant due to global SAVE statement"_warn_en_US,
           *specPartState_.saveInfo.saveAll, "Global SAVE statement"_en_US);
     } else if (auto msg{CheckSaveAttr(*symbol)}) {
       Say(name, std::move(*msg));

flang/test/Semantics/resolve45.f90

@@ -34,13 +34,13 @@ subroutine s3(x)
 end
 
 subroutine s4
-  !ERROR: Explicit SAVE of 'z' is redundant due to global SAVE statement
+  !WARNING: Explicit SAVE of 'z' is redundant due to global SAVE statement
   save z
   save
   procedure(integer), pointer :: x
-  !ERROR: Explicit SAVE of 'x' is redundant due to global SAVE statement
+  !WARNING: Explicit SAVE of 'x' is redundant due to global SAVE statement
   save :: x
-  !ERROR: Explicit SAVE of 'y' is redundant due to global SAVE statement
+  !WARNING: Explicit SAVE of 'y' is redundant due to global SAVE statement
   integer, save :: y
 end