unity: add linux port

This allows using unity fixture in Linux host tests

components/unity/unity_port_linux.c

@@ -0,0 +1,42 @@
+/*
+ * SPDX-FileCopyrightText: 2022 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+#include <string.h>
+#include <stdbool.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <sys/time.h>
+#include "unity.h"
+#include "sdkconfig.h"
+
+
+static struct timeval s_test_start, s_test_stop;
+
+void unity_putc(int c)
+{
+    putc(c, stdout);
+}
+
+void unity_flush(void)
+{
+    fflush(stdout);
+    fsync(fileno(stdout));
+}
+
+void unity_exec_time_start(void)
+{
+    gettimeofday(&s_test_start, NULL);
+}
+
+void unity_exec_time_stop(void)
+{
+    gettimeofday(&s_test_stop, NULL);
+}
+
+uint32_t unity_exec_time_get_ms(void)
+{
+    return (uint32_t) (((s_test_stop.tv_sec * 1000000ULL + s_test_stop.tv_usec) -
+                        (s_test_start.tv_sec * 1000000ULL + s_test_start.tv_usec)) / 1000);
+}