freertos: Added partial unit tests for Linux simulator

* The unit tests are derived from the FreeRTOS test app
  in components/freertos/test_apps/freertos. They are
  quite incompatible with the main test application, which
  is why they have been placed under
  tools/test_apps/linux_compatible/linux_freertos for now.

tools/test_apps/linux_compatible/linux_freertos/main/Kconfig.projbuild

@@ -0,0 +1,36 @@
+menu "IDF unit test"
+
+    config UNITY_FREERTOS_PRIORITY
+        int "Priority of Unity test task"
+        default 5
+
+    config UNITY_FREERTOS_CPU
+        int "CPU to run Unity test task on"
+        default 0
+
+    config UNITY_FREERTOS_STACK_SIZE
+        int "Stack size of Unity test task, in bytes"
+        default 8192
+
+    config UNITY_WARN_LEAK_LEVEL_GENERAL
+        int "Leak warning level"
+        default 255
+
+    config UNITY_CRITICAL_LEAK_LEVEL_GENERAL
+        int "Critical leak"
+        default 1024
+
+    config UNITY_CRITICAL_LEAK_LEVEL_LWIP
+        int "Critical leak for UT which use LWIP component"
+        default 4095
+
+    config UNITY_IGNORE_PERFORMANCE_TESTS
+        bool "Ignore performance test results"
+        default y if IDF_ENV_FPGA
+        default n
+        help
+            If set, performance tests that use TEST_PERFORMANCE_LESS_THAN and
+            TEST_PERFORMANCE_GREATER_THAN macros will log the performance value
+            but not fail the test if the threshold is not met.
+
+endmenu