libevp-agent and libevp-app-sdk Makefiles

These Makefiles are called recursively by the top-level Makefile, and they use a structure based on the Kbuild system. They use a macro called obj-y to collect the list of objects required to build the library. The value of this macro is composed of several statements, such as:

obj-y += agent_event.o
obj-$(CONFIG_EVP_MODULE_IMPL_DOCKER) += docker.o

The first statement obj-y += agent_event.o adds the object file called agent_event.o to the obj-y list, but the second statement obj-$(CONFIG_EVP_MODULE_IMPL_DOCKER) += docker.o adds conditionally the object docker.o based in the value of the macro CONFIG_EVP_MODULE_IMPL_DOCKER, which derives from the .config file generated in the config target. This structure simplifies the Makefile and avoids complex if-else chains as every Kconfig option becomes a conditional statement. If the Kconfig value is not set, or it is set to a value different than y, then the list of objects will not be added to obj-y but to obj- or obj-n keeping them out of the final list of objects used to build the libraries.

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