SUBDIRS= replacement

[Christoph Hellwig]

Hi Masahiro, hi Michal,

I just got this beatiful warning:

hch@carbon:~/work/xfs$ make -j4 SUBDIRS=fs/xfs
Makefile:189: ================= WARNING ================
Makefile:190: 'SUBDIRS' will be removed after Linux 5.3
Makefile:191: Please use 'M=' or 'KBUILD_EXTMOD' instead
Makefile:192: ==========================================

Both the replacement seem to be geared towards building externals
modules.  But what is the replacement for just building a directory
of the normal kernel tree?

E.g. what hit this is that I rebased an XFS series, and wanted to
compile test just the xfs code for each step using

make -j4 SUBDIRS=fs/xfs