Document rename_replace_existing macro

Author: dgreen-arm

library/psa_its_file.c

@@ -62,9 +62,12 @@
 #define PSA_ITS_MAGIC_STRING "PSA\0ITS\0"
 #define PSA_ITS_MAGIC_LENGTH 8
 
+/* As rename fails on Windows if the new filepath already exists,
+ * use MoveFileExA with the MOVEFILE_REPLACE_EXISTING flag instead.
+ * Returns 0 on success, nonzero on failure. */
 #if defined(_WIN32)
 #define rename_replace_existing( oldpath, newpath ) \
-    (!MoveFileExA( oldpath, newpath, MOVEFILE_REPLACE_EXISTING ))
+    ( ! MoveFileExA( oldpath, newpath, MOVEFILE_REPLACE_EXISTING ) )
 #else
 #define rename_replace_existing( oldpath, newpath ) rename( oldpath, newpath )
 #endif