The JDK build system includes some specific hooks and files to allow the building of Oracle's Java SE Embedded product. These details are not relevant to the OpenJDK and we propose to move them out of the OpenJDK repository.

To do this we need a way to allow the build rules/definitions/targets to be customized/specialized by the inclusion of other build files. It is impractical, if not impossible, to allow completely arbitrary specialization due to the way build files get included and combined so we are looking at a very simple mechanism which is initially only employed in those locations where the SE Embedded specialization currently exists.

The basic approach is to define CUSTOM_MAKE_DIR to be the root location for an additional set of build files, and to set this to be the Oracle make/closed repository by default when not doing an OpenJDK build. We then use the -include mechanism to include specific files at specific places if they exist (the -include mechanism, in contrast to the include mechanism does not report an error if the file does not exist: this avoids the need to perform existance tests.