Add ESP_PLATFORM to build environment.

Merges https://github.com/espressif/esp-idf/pull/2601

tools/cmake/scripts/expand_requirements.cmake

@@ -33,6 +33,8 @@ cmake_minimum_required(VERSION 3.5)
 include("${IDF_PATH}/tools/cmake/utilities.cmake")
 include("${IDF_PATH}/tools/cmake/component_utils.cmake")
 
+set(ESP_PLATFORM 1)
+
 if(NOT DEPENDENCIES_FILE)
     message(FATAL_ERROR "DEPENDENCIES_FILE must be set.")
 endif()

tools/idf.py

@@ -165,7 +165,7 @@ def _ensure_build_directory(args, always_run_cmake=False):
         if args.generator is None:
             args.generator = detect_cmake_generator()
         try:
-            cmake_args = ["cmake", "-G", args.generator, "-DPYTHON_DEPS_CHECKED=1"]
+            cmake_args = ["cmake", "-G", args.generator, "-DPYTHON_DEPS_CHECKED=1", "-DESP_PLATFORM=1"]
             if not args.no_warnings:
                 cmake_args += ["--warn-uninitialized"]
             if args.no_ccache: