Use Portage config directly from src dir

Instead of copying the Portage configuration files to `/etc/portage` and
`/usr/${target}/etc/portage`, the build scripts now use the
configuration directories from the source directory.  This avoids issues
with changes (especially removal of files) getting propagated to the
actual configuration paths.

prepare.sh

@@ -13,16 +13,16 @@ fi
 chown portage: "$(portageq envvar DISTDIR)"
 
 ARCH=$(PORTAGE_CONFIGROOT=/usr/${target} portageq envvar ARCH)
+PKGDIR=$(portageq envvar PKGDIR)
+FEATURES="${FEATURES} binpkg-multi-instance"
 
-if [ -f /usr/${target}/etc/portage/make.conf ]; then
-    sed -i '/PKGDIR=/d' /usr/${target}/etc/portage/make.conf
-fi
 # For some reason, libcap installs its pkg-config files in the wrong
 # place.  More strangely, even though `PKG_CONFIG_PATH` contains that
 # directory, `pkg-config` does not find the `.pc` files for libcap.
 # We work around this by merging /usr/lib64/pkgconfig and
 # /usr/lib/pkgconfig.
-FEATURES="${FEATURES} binpkg-multi-instance" \
+FEATURES="${FEATURES}" \
+PKGDIR="${PKGDIR}" \
 ${target}-emerge -kb1vnj sys-libs/libcap
 if [ -d /usr/${target}/usr/lib/pkgconfig ] \
         && [ ! -d /usr/${target}/usr/lib64/pkgconfig ]; then
@@ -30,32 +30,35 @@ if [ -d /usr/${target}/usr/lib/pkgconfig ] \
     ln -snf ../lib64/pkgconfig /usr/${target}/usr/lib/pkgconfig
 fi
 
-if [ ! -d /usr/${target}/etc/portage/make.conf ]; then
-    mv /usr/${target}/etc/portage/make.conf \
-        /usr/${target}/etc/portage/make.conf.orig
-    sed -ri 's: ?-pam::' /usr/${target}/etc/portage/make.conf.orig
-    ls -l /usr/${target}/etc/portage
-    mkdir /usr/${target}/etc/portage/make.conf
-    mv /usr/${target}/etc/portage/make.conf.orig \
-        /usr/${target}/etc/portage/make.conf/10-base.conf
-fi
-
-if [ ! -d /etc/portage/make.conf ]; then
-    mv /etc/portage/make.conf \
-        /etc/portage/make.conf.orig
-    mkdir /etc/portage/make.conf
-    mv /etc/portage/make.conf.orig \
-        /etc/portage/make.conf/10-base.conf
+if [ ! -f portage/make.conf/10-crossdev.conf ]; then
+    sed -r \
+        -e 's: ?-pam::' \
+        -e '/PKGDIR=/d' \
+        /usr/${target}/etc/portage/make.conf \
+        > portage/config/target/etc/portage/make.conf/10-crossdev.conf
 fi
 
 ln -snf /var/db/repos/gentoo/profiles/default/linux/${ARCH}/17.0 \
     /usr/${target}/etc/portage/make.profile
 
+FEATURES="${FEATURES}" \
+PKGDIR="${PKGDIR}" \
 ${target}-emerge -bk1nvj sys-libs/glibc
 
+FEATURES="${FEATURES}" \
+PKGDIR=$(portageq envvar PKGDIR) \
+USE=pam \
 ${target}-emerge -bknvj sys-apps/util-linux
 
 # Migrate to the merged-usr layout
 mkdir -p /usr/${target}/bin
 emerge -bknv --quiet-build=y merge-usr
 merge-usr --root=/usr/${target}
+
+# Set the Portage profile
+ln -snf \
+    /var/db/repos/gentoo/profiles/${profile} \
+    portage/config/target/etc/portage/make.profile
+ln -snf \
+    $(realpath /etc/portage/make.profile) \
+    portage/config/host/etc/portage/make.profile