prep/errors: fix absolute paths handling issues on Windows

Absolute paths on Windows can be hard to predict (C:\foo, C:/foo,
c:\foo, ...) and thus to remove in a robust way. Instead of trying to
post-process them, do not include them in baselines in the first place.

Also remove the test driver mechanism we introduced just for that case.

testsuite/drivers/base_driver.py

@@ -118,12 +118,6 @@ def output_refiners(self):
         if self.test_env.get("canonicalize_directory_separators", False):
             result.append(Substitute("\\", "/"))
 
-        # If requested, replace occurences of the working directory
-        if self.test_env.get("canonicalize_working_dir", False):
-            result.append(
-                Substitute(self.working_dir(), "[working-dir]")
-            )
-
         return result
 
     @property

testsuite/tests/prep/errors/main.adb

@@ -26,7 +26,24 @@ procedure Main is
       New_Line;
       if U.Has_Diagnostics then
          for D of U.Diagnostics loop
-            Put_Line (U.Format_GNU_Diagnostic (D));
+
+            --  Remove absolute paths from error messages to have consistent
+            --  baselines.
+
+            declare
+               Msg    : constant String := U.Format_GNU_Diagnostic (D);
+               Prefix : constant String :=
+                 "no_such_file.adb: Cannot open ";
+            begin
+               if Msg'Length > Prefix'Length
+                  and then Msg (Msg'First .. Msg'First + Prefix'Length - 1)
+                           = Prefix
+               then
+                  Put_Line (Prefix & "[...]");
+               else
+                  Put_Line (Msg);
+               end if;
+            end;
          end loop;
          New_Line;
       end if;

testsuite/tests/prep/errors/test.out

@@ -13,7 +13,7 @@ PragmaNodeList[1:1-1:19]
 
 == no_such_file.adb ==
 
-no_such_file.adb: Cannot open [working-dir]/no_such_file.adb
+no_such_file.adb: Cannot open [...]
 
 CompilationUnitList[1:1-1:1]: <empty list>
 

testsuite/tests/prep/errors/test.yaml

@@ -1,5 +1,4 @@
 driver: ada-api
 main: main.adb
-canonicalize_working_dir: true
 control:
     - [XFAIL, "valgrind", "Pending resolution of eng/gpr/gpr-issues#43"]