Fail to build Linux with O= in master

[Julien Grall]

Hello,

I have tried to build the latest master and got the following error:

42sh> make O=~/works/linux-build/aarch64-4k -C ~/works/linux                                                                                                     
make: Entering directory '/home/julgra01/works/linux'
Makefile:135: *** failed to create output directory "~/works/linux-build/aarch64-4k".  Stop.
make: Leaving directory '/home/julgra01/works/linux'

The bisector found the commit 8e9b466 "kbuild: use $(abspath ...)
instead of $(shell cd ... && /bin/pwd)".

Looking at the code, it seems that it is because the code is
now using $(realpath ...). Indeed when I replace ~ by $HOME
the kernel is now built.

I am not a Makefile expert, so I would appreciate if anyone
could suggest a patch for this.

Regards,

-- 
Julien Grall