[build] Allow for named configurations at build time
Allow named configurations to be specified via the CONFIG=... build
parameter. For headers in config/*.h which support named
configurations, the following files will be included when building
with CONFIG=<name>:
- config/defaults/<platform>.h (e.g. config/defaults/pcbios.h)
- config/<header>.h
- config/<name>/<header>.h (only if the directory config/<name> exists)
- config/local/<header>.h (autocreated if necessary)
- config/local/<name>/<header>.h (autocreated if necessary)
This mechanism allows for predefined named configurations to be
checked in to the source tree, as a directory config/<name> containing
all of the required header files.
The mechanism also allows for users to define multiple local
configurations, by creating header files in the directory
config/local/<name>.
Note that the config/*.h files which are used only to configure
internal iPXE APIs (e.g. config/ioapi.h) cannot be modified via a
named configuration. This avoids rebuilding the entire iPXE codebase
whenever switching to a different named configuration.
Inspired-by: Robin Smidsrød <robin@smidsrod.no>
Tested-by: Robin Smidsrød <robin@smidsrod.no>
Signed-off-by: Michael Brown <mcb30@ipxe.org>
Michael Brown