BUILD can be instructed to build an entire source tree recursively using a dirs file. This file resides in a directory that contains subdirectories (for example, at the root of a source code tree or subtree). Each subdirectory can be a source directory or another source tree. A dirs file should exist at the root of each source code subtree, and a sources file should exist in each “leaf” directory (that is, directories containing actual source code).
You can define the following macros in a dirs file:
DIRS
Contains a list of subdirectories to be built unconditionally. Entries in this list are separated by spaces or tabs.
OPTIONAL_DIRS
Contains a list of subdirectories to be built only if they are explicitly specified on the original BUILD command line.
By default, BUILD causes all x86 compilations to occur at warning level 3. You can override this warning level by defining the following in the sources file:
386_WARNING_LEVEL=-W4