Fix warnings where undefined vars are used.
Make Kconfig emit "FOO=" for unset bool options
To ensure make variables are always defined, even if empty.
When writing auto.conf, include symbols disabled by dependency to make sure all make variables are always defined.
Fixesespressif/esp-idf#137
Cherry-picked from https://github.com/espressif/esp-idf/pull/138
Extra space is needed in echo -n "-lncurses ", otherwise if pkg-config outputs a directory after that, it will result in "-lncurses-L/opt/local/lib" (without space).
-Wno-format-security flag is needed on macOS to silence warnings about printf(gettext("message")) constructs.
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.
krzychb