cmake: Refactor bootloader_subproject into the bootloader component itself

components/bootloader/project_include.cmake

@@ -0,0 +1,31 @@
+if(IS_BOOTLOADER_BUILD)
+  return()  # don't keep recursing!
+endif()
+
+# Glue to build the bootloader subproject binary as an external
+# cmake project under this one
+#
+#
+set(bootloader_build_dir "${CMAKE_BINARY_DIR}/bootloader")
+set(bootloader_binary_files
+  "${bootloader_build_dir}/bootloader.elf"
+  "${bootloader_build_dir}/bootloader.bin"
+  "${bootloader_build_dir}/bootloader.map"
+  )
+
+ExternalProject_Add(bootloader
+  # TODO: support overriding the bootloader in COMPONENT_PATHS
+  SOURCE_DIR "${IDF_PATH}/components/bootloader/subproject"
+  BINARY_DIR "${bootloader_build_dir}"
+  CMAKE_ARGS -DSDKCONFIG=${SDKCONFIG} -DIDF_PATH="${IDF_PATH}"
+  INSTALL_COMMAND ""
+  BUILD_ALWAYS 1  # no easy way around this...
+  BUILD_BYPRODUCTS ${bootloader_binary_files}
+  )
+
+# this is a hack due to an (annoying) shortcoming in cmake, it can't
+# extend the 'clean' target to the external project
+# see thread: https://cmake.org/pipermail/cmake/2016-December/064660.html
+#
+# So for now we just have the top-level build remove the final build products...
+set_property(DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}" APPEND PROPERTY ADDITIONAL_MAKE_CLEAN_FILES ${bootloader_binary_files})

components/bootloader/subproject/CMakeLists.txt

@@ -12,8 +12,7 @@ set(BOOTLOADER_BUILD 1)
 set(IS_BOOTLOADER_BUILD 1)  # deprecated, use BOOTLOADER_BUILD
 add_definitions(-DBOOTLOADER_BUILD=1)
 
-set(MAIN_SRCS main/bootloader_start.c
-  main/flash_qio_mode.c)
+set(MAIN_SRCS main/bootloader_start.c)
 
 include($ENV{IDF_PATH}/tools/cmake/project.cmake)