C front-end: Record extern declarations in current scope

Previously, extern declarations would only be recorded in the global scope.
While they do belong to the global scope, they still need to take precedence in
name lookups in the local/current scope as well.

Also removing an unnecessary iostream include.

Fixes: diffblue#1867

regression/cbmc/extern1/main.c

@@ -0,0 +1,31 @@
+#include <stdio.h>
+#include <assert.h>
+
+int some_global = 10;
+
+void shadow()
+{
+  int some_global = 5;
+
+  printf("local: %d\n", some_global);
+  {
+    int some_global = 0;
+    ++some_global;
+    printf("local2: %d\n", some_global);
+  }
+
+  printf("local: %d\n", some_global);
+  {
+    extern int some_global;
+    ++some_global;
+    printf("global: %d\n", some_global);
+    assert(some_global == 11);
+  }
+
+  assert(some_global == 5);
+}
+
+int main(void)
+{
+  shadow();
+}

regression/cbmc/extern1/test.desc

@@ -0,0 +1,7 @@
+CORE
+main.c
+
+^EXIT=0$
+^SIGNAL=0$
+^VERIFICATION SUCCESSFUL$
+--

regression/cbmc/extern2/main.c

@@ -0,0 +1,20 @@
+#include <stdio.h>
+#include <assert.h>
+
+int param;
+void function(int param)
+{
+  printf("%d\n", param);
+  {
+    extern int param;
+    printf("%d\n", param);
+    assert(param == 2);
+  }
+  assert(param == 1);
+}
+
+int main(void)
+{
+  param = 2;
+  function(1);
+}

regression/cbmc/extern2/test.desc

@@ -0,0 +1,7 @@
+CORE
+main.c
+
+^EXIT=0$
+^SIGNAL=0$
+^VERIFICATION SUCCESSFUL$
+--

src/ansi-c/ansi_c_parser.cpp

@@ -8,8 +8,6 @@ Author: Daniel Kroening, [email protected]
 
 #include "ansi_c_parser.h"
 
-#include <iostream>
-
 #include "c_storage_spec.h"
 
 ansi_c_parsert ansi_c_parser;
@@ -35,8 +33,6 @@ ansi_c_id_classt ansi_c_parsert::lookup(
 
     if(n_it!=it->name_map.end())
     {
-      assert(id2string(n_it->second.prefixed_name)==
-             it->prefix+id2string(scope_name));
       identifier=n_it->second.prefixed_name;
       return n_it->second.id_class;
     }
@@ -150,6 +146,9 @@ void ansi_c_parsert::add_declarator(
     ansi_c_identifiert &identifier=scope.name_map[base_name];
     identifier.id_class=id_class;
     identifier.prefixed_name=prefixed_name;
+
+    if(force_root_scope)
+      current_scope().name_map[base_name] = identifier;
   }
 
   ansi_c_declaration.declarators().push_back(new_declarator);