adds extern "C" to the header files that were missing it. (#5857)

scripts/style_api_gen.py

@@ -631,6 +631,11 @@ print(HEADING)
 print('#ifndef LV_OBJ_STYLE_GEN_H')
 print('#define LV_OBJ_STYLE_GEN_H')
 print()
+print('''\
+#ifdef __cplusplus
+extern "C" {
+#endif
+''')
 print("#include \"../misc/lv_area.h\"")
 print("#include \"../misc/lv_style.h\"")
 print("#include \"../core/lv_obj_style.h\"")
@@ -648,6 +653,12 @@ for p in props:
 guard_close()
 
 print()
+print('''\
+#ifdef __cplusplus
+} /* extern "C" */
+#endif
+''')
+
 print('#endif /* LV_OBJ_STYLE_GEN_H */')
 
 sys.stdout = open(base_dir + '/../src/core/lv_obj_style_gen.c', 'w')
@@ -678,6 +689,11 @@ print(HEADING)
 print('#ifndef LV_STYLE_GEN_H')
 print('#define LV_STYLE_GEN_H')
 print()
+print('''\
+#ifdef __cplusplus
+extern "C" {
+#endif
+''')
 
 for p in props:
   guard_proc(p)
@@ -690,6 +706,11 @@ for p in props:
 guard_close()
 
 print()
+print('''\
+#ifdef __cplusplus
+} /* extern "C" */
+#endif
+''')
 print('#endif /* LV_STYLE_GEN_H */')
 
 sys.stdout = open(base_dir + '/../docs/overview/style-props.rst', 'w')