Instrument.C: Remap_Scopes only once

The scope remapping was implemented in a loop over
UIC.Instrumented_Entities, meaning that we were remapping them several
time. One time is enough, so extract this code of the loop.

Author: Jugst3r

testsuite/tests/subp_of_interest_c/test.py

@@ -1,6 +1,8 @@
 """
 Check that the subprograms of interest mechanism works as expected on a C
-example.
+example. It also acts as a regression testcase as gnatcov used to crash when
+instrumenting a source including multiple headers, with at last one of them
+not having any coverage obligation.
 """
 
 import os

tools/gnatcov/instrument-c.adb

@@ -3294,23 +3294,23 @@ package body Instrument.C is
                --  Associate these bit maps to the corresponding CU
 
                Set_Bit_Maps (UIC.CUs.Element (SFI), Bit_Maps);
+            end;
+         end loop;
 
-               --  Iterate through the package level body entities
+         --  Iterate through the package level body entities
 
-               Remap_Scopes (UIC.Scopes, SCO_Map);
+         Remap_Scopes (UIC.Scopes, SCO_Map);
 
-               for C in UIC.Scopes.Iterate loop
-                  declare
-                     CU : constant Created_Unit_Maps.Cursor :=
-                       UIC.CUs.Find (Scopes_In_Files_Map.Key (C));
-                  begin
-                     if Created_Unit_Maps.Has_Element (CU) then
-                        Set_Scope_Entities
-                          (Created_Unit_Maps.Element (CU),
-                           Scopes_In_Files_Map.Element (C).Scope_Entities);
-                     end if;
-                  end;
-               end loop;
+         for C in UIC.Scopes.Iterate loop
+            declare
+               CU : constant Created_Unit_Maps.Cursor :=
+                 UIC.CUs.Find (Scopes_In_Files_Map.Key (C));
+            begin
+               if Created_Unit_Maps.Has_Element (CU) then
+                  Set_Scope_Entities
+                    (Created_Unit_Maps.Element (CU),
+                     Scopes_In_Files_Map.Element (C).Scope_Entities);
+               end if;
             end;
          end loop;
       end;