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>

libc: remove now unneeded do_libc_headers

do_libc_headers is now a noop, and is no longer used, so remove that step.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

libc/glibc-eglibc: misc janitorial cleanups.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

libc/glibc: add glibc specifics to the shared code, and use it

Final step at sharing code between glibc and eglibc.
Fall, wall of shame, fall!... :-)

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

scripts: PARALLELMFLAGS is evil, rename

The reunification of the glibc/eglibc code paths exposed a nasty
bug in the glibc build: use of PARALLELMFLAGS breaks the build.

See the explanations in that bug report against FC6:
https://bugzilla.redhat.com/show_bug.cgi?format=multiple&id=212111

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

libc/glibc: commonalise assembling the list of addons

glibc and eglibc each have two very similar ways of building this list.
This can, and should definitetly, be shared.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

libc/glibc: commonalise setting of the minimum supported kernel version

It will be possible to use that also with eglibc, so this hunk belongs to
the common code.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

libc/glibc: use the common start_files procedure

Use the common procedure, shared between glibc and eglibc. This requires
that glibc-specific bits be included in the shared procedure.

But still build the full libc with the glibc-specific procedure. This will
be commonalised in a future commit.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

libc/eglibc: cleanup common code for sharing with glibc

Some stuff is eglibc-specific, so needs to be conditonal.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

libc/eglibc: move generic code to a common file

The build procedure for eglibc is generic enough to
be shared between glibc and eglibc. This includes:
- headers install (empty!)
- start files build
- complete libc build
- libc finish (empty!)
- add-ons list

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>