sys-apps/portage: Bump to version 2.3.77

sys-apps/portage: Bump to version 2.3.77

 #220533 Fix FEATURES=skiprocheck read-only DISTDIR support
 #646898 Support GLEP 75 mirror structure
 #658648 Disable emerge --autounmask by default, except for package.use
         and package.license changes
 #695870 Improvements to ebuild(5) man page

Bug: https://bugs.gentoo.org/697734
Bug: https://bugs.gentoo.org/220533
Bug: https://bugs.gentoo.org/646898
Bug: https://bugs.gentoo.org/658648
Bug: https://bugs.gentoo.org/695870
Package-Manager: Portage-2.3.77, Repoman-2.3.17
Signed-off-by: Zac Medico <zmedico@gentoo.org>