[hal] Add HAL_GetLastError to enable better error messages from HAL calls (#3320)

This uses thread local storage so a full error string can be provided, not just an error code.

hal/src/main/native/cpp/ErrorHandling.cpp

@@ -0,0 +1,41 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+#include <wpi/SmallString.h>
+#include <wpi/Twine.h>
+
+#include "hal/Errors.h"
+#include "hal/HALBase.h"
+
+namespace {
+struct LastErrorStorage {
+  int32_t status;
+  wpi::SmallString<512> message;
+};
+}  // namespace
+
+static LastErrorStorage& GetThreadLastError() {
+  thread_local LastErrorStorage lastError;
+  return lastError;
+}
+
+namespace hal {
+void SetLastError(int32_t status, const wpi::Twine& value) {
+  LastErrorStorage& lastError = GetThreadLastError();
+  lastError.message.clear();
+  value.toVector(lastError.message);
+  lastError.status = status;
+}
+}  // namespace hal
+
+extern "C" {
+const char* HAL_GetLastError(int32_t* status) {
+  if (*status == HAL_USE_LAST_ERROR) {
+    LastErrorStorage& lastError = GetThreadLastError();
+    *status = lastError.status;
+    return lastError.message.c_str();
+  }
+  return HAL_GetErrorMessage(*status);
+}
+}  // extern "C"