cmake: reconfigure when .config changes

[r3wretrhy]

cmake: reconfigure when .config changes.

Summary

• Why change is necessary: config.h and CONFIG_* are generated at configure time. kconfig-tweak (and other out-of-band .config edits) do not go through the menuconfig target, so Ninja left a stale include/nuttx/config.h.
• What functional part of the code is being changed: CMakeLists.txt configure-depends for ${NUTTX_BINARY_DIR}/.config.
• How: CMAKE_CONFIGURE_DEPENDS on .config. That file is only rewritten when it is missing or the board defconfig path changes, so watching it does not loop.
• Related NuttX Issue: cmake system fails to update config.h #12322

Impact

• Is new feature added? Is existing feature changed? NO
• Impact on user (will user need to adapt to change)? NO
• Impact on build (will build process change)? YES. Ninja re-runs CMake after an out-of-band .config edit, which is what the reporter expected (Re-running CMake...).
• Impact on hardware (will arch(s) / board(s) / driver(s) change)? NO
• Impact on documentation (is update required / provided)? NO
• Impact on security (any sort of implications)? NO
• Impact on compatibility (backward/forward/interoperability)? NO. Unchanged .config still does not reconfigure.

Testing

I confirm that changes are verified on local setup and works as intended:

• Build Host(s): Windows 11, CMake 3.29.2, Ninja
• Target(s): cmake -P lock that CMakeLists.txt watches .config; a Ninja mini-project with the same CMAKE_CONFIGURE_DEPENDS one-liner

Testing logs before change:

gh search code repo:apache/nuttx CMAKE_CONFIGURE_DEPENDS
[]

Testing logs after change:

cmake -P _tmp_test_cfgdep.cmake
-- CMAKELISTS_WATCHES_DOTCONFIG

cmake --build mini/b   # after editing watched.txt
[0/1] Re-running CMake...
-- Configuring done (0.0s)
-- Generating done (0.0s)

PR verification Self-Check

• This PR introduces only one functional change.
• I have updated all required description fields above.
• My PR adheres to Contributing Guidelines and Documentation (git commit title and message, coding standard, etc).
• My PR is still work in progress (not ready for review).
• My PR is ready for review and can be safely merged into a codebase.

[github-actions]

MemBrowse Memory Report

No memory changes detected for:

• arduino-mega2560
• esp32-devkitc
• hifive1-revb
• mirtoo
• qemu-armv8a
• qemu-intel64
• rx65n-rsk2mb
• s698pm-dkit
• stm32-nucleo-f103rb