Used by mbedTLS to set MBEDTLS_CONFIG_FILE in all components.
This change sets CFLAGS/etc at the project level and then exports those
variables for components, rather than setting them independently each time
a component Makefile is invoked.
Fixes problems with Eclipse trying to build in directories it shouldn't.
This is a breaking change for existing repositories, they need to rename
any component Makefiles to component.mk and rename their references to
$(IDF_PATH)/make/component.mk to $(IDF_PATH)/make/component_common.mk
This commit fixes the case when new Kconfig configuration options were added and you run `make menuconfig`.
Previously this would first show console prompt to set values for new options, and then launch menuconfig.
Now this will just launch menuconfig.
New target is added, defconfig, which may be useful for non-interactive environments to set default values for
all new configuration options.
