3rdparty: Fix Makefile coding conventions
diff --git a/tests/scripts/check-files.py b/tests/scripts/check-files.py
index 255bed8..6e35f52 100755
--- a/tests/scripts/check-files.py
+++ b/tests/scripts/check-files.py
@@ -144,6 +144,7 @@
     heading = "Tabs present:"
     files_exemptions = frozenset([
         "Makefile",
+        "Makefile.inc",
         "generate_visualc_files.pl",
     ])
 
@@ -181,7 +182,7 @@
         self.setup_logger(log_file)
         self.files_to_check = (
             ".c", ".h", ".sh", ".pl", ".py", ".md", ".function", ".data",
-            "Makefile", "CMakeLists.txt", "ChangeLog"
+            "Makefile", "Makefile.inc", "CMakeLists.txt", "ChangeLog"
         )
         self.excluded_directories = ['.git', 'mbed-os']
         self.excluded_paths = list(map(os.path.normpath, [