`rules.make' optionally includes `$(topdir)/build/config.make', so you
can customize your build without CVS trying to commit your modified
`config-default.make' all the time. Platform-specific variables are
-defined in `$(topdir)/build/platforms/$(PLATFORM).make', where
-$(PLATFORM) is detected in config-default.make. (Currently, the only
+defined in `$(topdir)/build/platforms/$(BUILD_PLATFORM).make', where
+$(BUILD_PLATFORM) is detected in config-default.make. (Currently, the only
choices are linux.make and win32.make.)
The best way to learn what the configuration variables are is to read