Usage is simple:[...]
cd /path/to/kernel/src
mkdir ~/build/kernel
make O=~/build/kernel [Make options]
Please note: The O= syntax must be used for ALL invocations of make.
How it works:
If the O= option is used, or KBUILD_OUTPUT is set then a second invocation
of make happens in the output directory.
The second invocation of make uses VPATH to tell make where to locate
the files. Furthermore include options for gcc is modifyied to point
both in the directory where the kernel src is located, and in the
directory where the output files are located. The latter is used for
generated .h files.