gnat_compare: skip 'E' xrefs (reference to first private entity)

When comparing GNAT's xrefs with libadalang nameres, skip references
to the first private entity.

testsuite/ada/gnat_compare/xrefs.adb

@@ -213,10 +213,15 @@ package body Xrefs is
             raise Program_Error;
          end if;
 
-         --  Ignore "end of spec/body" xrefs, which point on the ending
+         --  Ignore "end of spec/body" xrefs (e/t), which point on the ending
          --  semicolon of an entity body. LAL won't support that.
+         --
+         --  Ignore "first private entity" (E) xref, which points on the first
+         --  private entity of a given package.
 
-         if Current_Xrefs /= null and then Type_Char not in 'e' | 't' then
+         if Current_Xrefs /= null
+         and then Type_Char not in 'e' | 't' | 'E'
+         then
             Current_Xrefs.Xrefs.Append
               (Xref_Type'(Ref_Sloc => (Line_Number (Line),
                                        Column_Number (Column)),

testsuite/tests/name_resolution/gnat_compare_2/prj.gpr

@@ -0,0 +1,4 @@
+project Prj is
+  for Source_Dirs use (".");
+  for Main use ("test.adb");
+end Prj;

testsuite/tests/name_resolution/gnat_compare_2/test.adb

@@ -0,0 +1,8 @@
+procedure Test is
+   package P is
+   private
+      type I is new Integer;
+   end P;
+begin
+   null;
+end Test;

testsuite/tests/name_resolution/gnat_compare_2/test.out

@@ -0,0 +1,13 @@
+== test.adb ==
+test.adb:1:11 => test.adb:1:11 (LAL: ok)
+test.adb:5:8 => test.adb:2:12 (LAL: ok)
+test.adb:8:5 => test.adb:1:11 (LAL: ok)
+
+Stats:
+GNAT xrefs have 3 entries
+LAL xrefs have:
+  * 3 OK entries (100.00%)
+  * 0 DIFFERENT entries (0.00%)
+  * 0 ERROR entries (0.00%)
+  * 0 MISSING entries (0.00%)
+  * 0 ADDITIONAL entries (0.00%)

testsuite/tests/name_resolution/gnat_compare_2/test.yaml

@@ -0,0 +1,2 @@
+driver: gnat-compare
+project_file: prj.gpr