config: add an option to name the sysroot directory
Depending on local policies, some users have expressed a need to
have the sysroot be named differently than the hard-coded name.
Add an option for that.
Default to 'sysroot' to match the existing literature.
While at it, replace 'sys-root' with 'sysroot' everywhere we
reference the sysroot.
Reported-by: Alexey Kuznetsov <Alexey.KUZNETSOV@youtransactor.com>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>