toolchain: add glibc support for ARCv2

toolchain: add glibc support for ARCv2

Finally there's working ARC port of glibc thanks to Vineet and Cuper!
This port is based on pretty recent glibc's master branch and ARC
changes are being reviewed now in glibc's mailing list.

Thus we again have to use sources from our GitHub but as soon as there's
a glibc release with our patches applied we'll switch to upstream releases
and will drop our glibc GitHub repo alltogether.

Note now we cut tags in glibc repo simultaneously with tags
in Binutils and GCC repos and so to make sure everything works in the best
way we plan to update glibc tag together with Binutils and GCC.

Also note as of today ARCompact (AKA ARCv1 ISA) is not supported in glibc
but we plan to fix it soonish so for now we make glibc intentionally
dependent on archs38.

Also note we are not creating directory "2.26" because all patches for glibc
ver 2.26 applies to arc glibc port.

Signed-off-by: Evgeniy Didin <didin@synopsys.com>
CC: Alexey Brodkin <abrodkin@synopsys.com>
CC: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
CC: Waldemar Brodkorb <wbx@openadk.org>
CC: Romain Naour <romain.naour@gmail.com>
Cc: Cupertino Miranda <cmiranda@synopsys.com>
Cc: Vineet Gupta <vgupta@synopsys.com>
Cc: Anton Kolesov <akolesov@synopsys.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>