Merge pull request #4749 from 0xc0170/fix_inc_paths

tools: fix toolchain extend inc paths

Author: 0xc0170

tools/toolchains/__init__.py

@@ -863,7 +863,10 @@ def compile_sources(self, resources, inc_dirs=None):
 
         inc_paths = resources.inc_dirs
         if inc_dirs is not None:
-            inc_paths.extend(inc_dirs)
+            if isinstance(inc_dirs, list):
+                inc_paths.extend(inc_dirs)
+            else:
+                inc_paths.append(inc_dirs)
         # De-duplicate include paths
         inc_paths = set(inc_paths)
         # Sort include paths for consistency