Avoid exporting variables in build scripts

Environment variables "pollute" the build environment of packages and
can affect their output.

This change results in the removal of some files from packages that
were not meant to be packaged. It also removes the need for a
workaround in automake 1.10.3 to manually remove such files.

Variables are now saved in an .env file for each system and included
in scripts that need them using the dot operation.

sysc/init

@@ -7,12 +7,13 @@
 
 set -e
 
-export PATH=/usr/bin:/usr/sbin
-export PREFIX=/usr
-export SOURCES=/usr/src
-export DESTDIR=/tmp/destdir
-export DISTFILES=/distfiles
-export SRCDIR="${SOURCES}"
+PREFIX=/usr
+SOURCES="${PREFIX}/src"
+DESTDIR=/tmp/destdir
+DISTFILES=/distfiles
+SRCDIR="${SOURCES}"
+
+export PATH="${PREFIX}/bin:${PREFIX}/sbin"
 export HOME=/tmp
 export SOURCE_DATE_EPOCH=0
 
@@ -61,4 +62,12 @@ ln -s /usr/bin/bash /usr/bin/sh
 
 # Begin sysc bootstrapping process
 cd "${SOURCES}"
+
+# shellcheck disable=SC2129
+echo "PREFIX=${PREFIX}" >> .env
+echo "SOURCES=${SOURCES}" >> .env
+echo "DESTDIR=${DESTDIR}" >> .env
+echo "DISTFILES=${DISTFILES}" >> .env
+echo "SRCDIR=${SRCDIR}" >> .env
+
 exec ./run.sh