from the absence of command-line arguments) to the src/build/localdefs.mk
file.

This insures that incremental builds (e.g. in src/sbbs3) use the same
build type (e.g. debug vs. release) as the intitial install. Unfortuantely
it also means that switching the build type later requires editing or
deleting the localdefs.mk file, which means new instructions for the wiki.