testsuite: Add --strip-trailing-cr to diff call

On Windows, git defaults to maintaining line endings, which means it
changed \n to \r\n on all files it identifies as text. And that includes
our test output.

Luckily diff(1) has an option to undo that. And since we do not care
about line endings in those tests, we can just use it.

testsuite/gsk/node-parser.c

@@ -75,7 +75,7 @@ diff_with_file (const char  *file1,
   process = g_subprocess_new (G_SUBPROCESS_FLAGS_STDIN_PIPE
                               | G_SUBPROCESS_FLAGS_STDOUT_PIPE,
                               error,
-                              "diff", "-u", file1, "-", NULL);
+                              "diff", "--strip-trailing-cr", "-u", file1, "-", NULL);
   if (process == NULL)
     return NULL;
 

testsuite/testutils.c

@@ -42,7 +42,7 @@ diff_with_file (const char  *file1,
   diff_cmd = g_find_program_in_path ("diff");
   if (diff_cmd)
     {
-      const char *command[] = { diff_cmd, "-u", file1, NULL, NULL };
+      const char *command[] = { diff_cmd, "--strip-trailing-cr", "-u", file1, NULL, NULL };
 
       if (len < 0)
         len = strlen (text);