Merge branch 'bugfix/make_config_problems' into 'master'

build system: Fix several make & configuration problems

Collection of quasi-related build system fixes:
* Fix issues with "make menuconfig" running twice when no existing sdkconfig
* Fix issues with menuconfig getting into a bad state if "make -jN" and no existing sdkconfig
* Hopefully fix intermittent issue with build system sometimes not picking up all config, leading to missing BT/WiFi libs at compile/link time.
* Fix issues with path resolution on Windows (including in Eclipse)
* Add new BATCH_BUILD variable for IDEs and automated build environments.

See merge request !485