arduino as component: Remove circular dependency around 'main'

[projectgus]

arduino-esp32 has to depend on main in autostart mode, for setup() and loop(),
but this can be done with undefined symbol entries to avoid a large dependency
cycle and other linker errors.

Closes espressif/esp-idf#6968

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[me-no-dev]

How do you know what is the proper mangle prefix/suffix? Asking because we might need to add some more functions to the list

[igrr]

You can run something like:

echo "void setup() {}" | g++ -c -x c++ -o - - | nm -

Output:

0000000000000000 T __Z5setupv

[me-no-dev]

@projectgus Unfortunately this change caused arduino to not find the other components. I guess this means that sdkconfig was not expanded when it ran through CMakeLists and the components were not "required"

[igrr]

@me-no-dev as I mentioned on Wednesday, this pattern:

arduino-esp32/CMakeLists.txt

Lines 169 to 178 in a9bd39d

	if(NOT CONFIG_ARDUINO_SELECTIVE_COMPILATION OR CONFIG_ARDUINO_SELECTIVE_ArduinoOTA)
	list(APPEND priv_requires esp_https_ota)
	endif()
	if(NOT CONFIG_ARDUINO_SELECTIVE_COMPILATION OR CONFIG_ARDUINO_SELECTIVE_LITTLEFS)
	if(CONFIG_LITTLEFS_PAGE_SIZE)
	list(APPEND priv_requires esp_littlefs)
	endif()
	endif()
	idf_component_register(INCLUDE_DIRS ${includedirs} PRIV_INCLUDE_DIRS ${priv_includes} SRCS ${srcs} REQUIRES ${requires} PRIV_REQUIRES ${priv_requires})

doesn't work in IDF build system. This is because IDF build system processes each component CMakeLists.txt twice:

1. first time, in a process called "early expansion", to determine component requirements. All arguments except REQUIRES and PRIV_REQUIRES that are passed to idf_component_register are ignored.
2. second time, when the components list is known, and CONFIG options are already expanded. At this stage, REQUIRES and PRIV_REQUIRES arguments are ignored.

Before this PR, arduino component had main as a requirement, while main implicitly required all components included into the build. Even though the lines in CMakeLists.txt which I linked above didn't do anything [1] (CONFIG_* items were not defined at the early expansion pass), this transitive dependency arduino -> main -> {every other component} caused the compilation to succeed.

Now that the dependency from arduino to every other component through main has been removed, arduino component dependencies on arduino_tinyusb, esp_littlefs, esp_https_ota no longer works.

I'll open a PR to correct this by adding these dependencies at a later stage in the component CMakeLists file.

Edit: [1]: i mistakenly said that the fragment didn't do anything. This isn't correct. It should be said that the linked CMakeLists.txt fragment always evaluated as if all of the Kconfig options were undefined, or set to "false". This means, for example, that NOT CONFIG_ARDUINO_SELECTIVE_COMPILATION evaluated as true.