xbps-src: infrastructure changes required for "nonfree" keyword in tmpls.

- The chroot target now execs masterdir/bin/xbps-shell to set up correct envvars.
- 2 pkgs are now in nonfree repo: adobe-flash-plugin and jre.
- Renamed some vars in xbps-src to be in uppercase, notably XBPS_MACHINE.
- make-repoidx target now creates the index for all "known" directories specified
  via XBPS_PACKAGESDIR: XBPS_MACHINE, noarch, and nonfree/XBPS_MACHINE.

srcpkgs/gcc/template

@@ -56,10 +56,10 @@ if [ -n "$BOOTSTRAP_PKG_REBUILD" ]; then
 	Add_dependency build flex
 fi
 
-if [ "${xbps_machine}" = "x86_64" ]; then
-	_triplet="${xbps_machine}-unknown-linux-gnu"
+if [ "${XBPS_MACHINE}" = "x86_64" ]; then
+	_triplet="${XBPS_MACHINE}-unknown-linux-gnu"
 else
-	_triplet="${xbps_machine}-pc-linux-gnu"
+	_triplet="${XBPS_MACHINE}-pc-linux-gnu"
 fi
 
 do_configure()
@@ -96,7 +96,7 @@ do_build()
 
 do_install()
 {
-	if [ "$xbps_machine" = "x86_64" ]; then
+	if [ "$XBPS_MACHINE" = "x86_64" ]; then
 		vmkdir usr/lib
 		cd ${DESTDIR}/usr && ln -sf lib lib64 && cd ${wrksrc}
 	fi