Unset diff.ignoreSubmodules=all when running gclient sync.

Bug: 1470195
Change-Id: I1317e5f12d6cc7fae44b2a463ddf6d0f85629759
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/4767516
Reviewed-by: Josip Sokcevic <sokcevic@chromium.org>
Commit-Queue: Joanna Wang <jojwang@chromium.org>
diff --git a/gclient_scm.py b/gclient_scm.py
index 8743f71..60958b5 100644
--- a/gclient_scm.py
+++ b/gclient_scm.py
@@ -583,13 +583,14 @@
         config = subprocess2.capture(
             ['git', 'config', '-l'],
             cwd=args[0].checkout_path).decode('utf-8').strip().splitlines()
-        if 'diff.ignoresubmodules=all' not in config:
-          subprocess2.capture(['git', 'config', 'diff.ignoreSubmodules', 'all'],
-                              cwd=args[0].checkout_path).strip()
+        if 'diff.ignoresubmodules=all' in config:
+          subprocess2.capture(
+              ['git', 'config', '--unset', 'diff.ignoreSubmodules'],
+              cwd=args[0].checkout_path)
         if 'fetch.recursesubmodules=off' not in config:
           subprocess2.capture(
               ['git', 'config', 'fetch.recurseSubmodules', 'off'],
-              cwd=args[0].checkout_path).strip()
+              cwd=args[0].checkout_path)
       return return_val
 
     return wrapper