[wpilibc] Add FRC_ReportWarning (#6681)

wpilibc/src/main/native/include/frc/Errors.h

@@ -142,6 +142,17 @@ namespace warn {
     }                                                                    \
   } while (0)
 
+/**
+ * Reports a warning to the driver station (using HAL_SendError).
+ *
+ * @param[in]  format error message format
+ */
+#define FRC_ReportWarning(format, ...)                                  \
+  do {                                                                  \
+    ::frc::ReportError(warn::Warning, __FILE__, __LINE__, __FUNCTION__, \
+                       FMT_STRING(format) __VA_OPT__(, ) __VA_ARGS__);  \
+  } while (0)
+
 /**
  * Makes a runtime error exception object. This object should be thrown
  * by the caller.