Merge remote-tracking branch 'origin/pr/2637' into mbedtls-2.16

* origin/pr/2637:
  Only use submodule if present
diff --git a/scripts/abi_check.py b/scripts/abi_check.py
index f837f7a..30c3fe5 100755
--- a/scripts/abi_check.py
+++ b/scripts/abi_check.py
@@ -148,7 +148,8 @@
         my_environment = os.environ.copy()
         my_environment["CFLAGS"] = "-g -Og"
         my_environment["SHARED"] = "1"
-        my_environment["USE_CRYPTO_SUBMODULE"] = "1"
+        if os.path.exists(os.path.join(git_worktree_path, "crypto")):
+            my_environment["USE_CRYPTO_SUBMODULE"] = "1"
         make_output = subprocess.check_output(
             [self.make_command, "lib"],
             env=my_environment,