Then, Kconfig shapes the Makefile


Using the "y" trick you turn 3-lines conditionals into 1 line
obj-$(CONFIG_FOO) += foo.o
cflags-$(CONFIG_BAR) += -DBAR

Kconfig appears to suggest use of #ifdef/#endif
Please avoid #ifdef, it's the source of most bugs in C

With proper Kconfig values (int, not bool) you can do better
Remember that no code is emitted for "if (0)" blocks

If any, can turn #ifdef into a constant in your own file

Possibly, use the compiler's help
__builtin_constant_p() for example