sys-devel/gcc-config: bump up to 2.1

sys-devel/gcc-config: bump up to 2.1

- Don't cleanup /lib/libunwind.so (bug #667020)
- Drop GCC_PATH reconstruction (bug #174422)
- Use findmnt for mountpoint check when available (bug #693588)
- drop /etc/env.d/gcc/.NATIVE symlink
- drop /etc/env.d/gcc/config migration code
- drop empty /etc/env.d/05gcc-${CTARGET} files
- add einfo logging around library backup

Bug: https://bugs.gentoo.org/667020
Bug: https://bugs.gentoo.org/174422
Bug: https://bugs.gentoo.org/693588
Package-Manager: Portage-2.3.75, Repoman-2.3.17
Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>