[flang] Fix one regression failure related to BIND(C) statement

For BIND(C) statement, two common block with the same name can have the
same bind name. Fix the regression failure by adding this check. Also add
the regression tests.

Co-authored-by: Jean Perier <jperier@nvidia.com>

Reviewed By: clementval

Differential Revision: https://reviews.llvm.org/D127841

flang/lib/Semantics/check-declarations.cpp

@@ -1892,7 +1892,10 @@ void CheckHelper::CheckBindC(const Symbol &symbol) {
     auto pair{bindC_.emplace(*name, symbol)};
     if (!pair.second) {
       const Symbol &other{*pair.first->second};
-      if (DefinesBindCName(other) && !context_.HasError(other)) {
+      // Two common blocks with the same name can have the same BIND(C) name.
+      if ((!symbol.has<CommonBlockDetails>() ||
+              symbol.name() != other.name()) &&
+          DefinesBindCName(other) && !context_.HasError(other)) {
         if (auto *msg{messages_.Say(symbol.name(),
                 "Two symbols have the same BIND(C) name '%s'"_err_en_US,
                 *name)}) {

flang/test/Semantics/declarations03.f90

@@ -48,3 +48,24 @@ module m
   integer, bind(c, name="ss2") :: s5
 
 end
+
+subroutine common1()
+  real :: x
+  common /com/ x
+  bind(c, name='xcom') /com/ ! no error
+end subroutine
+
+subroutine common2()
+  real :: x
+  common /com/ x
+  bind(c, name='xcom') /com/ ! no error
+end subroutine
+
+module a
+  integer, bind(c, name="int") :: i
+end module
+
+module b
+  !ERROR: Two symbols have the same BIND(C) name 'int'
+  integer, bind(c, name="int") :: i
+end module