portage: Provide a base Portage configuration

Instead of requiring every Aimee OS project to carry around a full
Portage configuration tree, including patches, saved configurations,
etc., we now support a "layered" configuration system.  Aimee OS core
provides a base configuration that includes all settings, patches, etc.
common for all Aimee OS projects.  At build time, this base
configuration is combined with the project's configuration, which need
only specify USE flags, etc. for that specific project.  This should
make maintenance across multiple projects easier, and make getting a new
project started _significantly_ less cumbersome.

portage/make.conf/20-binpkgs.conf

@@ -0,0 +1,2 @@
+FEATURES="${FEATURES} binpkg-multi-instance buildpkg"
+EMERGE_DEFAULT_OPTS="${EMERGE_DEFAULT_OPTS} --usepkg --binpkg-respect-use=y"

portage/make.conf/30-default-use.conf

@@ -0,0 +1 @@
+USE='-man -doc minimal pam zstd'

portage/make.conf/40-goarch.conf

@@ -0,0 +1,2 @@
+GOOS=linux
+GOARCH=${ARCH}

portage/make.conf/40-lang.conf

@@ -0,0 +1,3 @@
+LINGUAS=en
+L10N=en-US
+USE="${USE} -nls"

portage/make.conf/80-quiet.conf

@@ -0,0 +1,2 @@
+EMERGE_DEFAULT_OPTS="${EMERGE_DEFAULT_OPTS} --quiet-build=y"
+FEATURES="${FEATURES} -news"