toolchain: add a hidden config option to enable the toolchain package

The usual way to enable a package using the package infrastructure is to
use a config option so instead to add the toolchain package to the
TARGETS variable in the Makefile add a config option like all the other
toolchain packages.

[Thomas: remove comment that no longer made sense in the main
Makefile, and add a comment above the new hidden Config.in option to
explain what it is useful for.]

Signed-off-by: Fabio Porcedda <fabio.porcedda@gmail.com>
Cc: Arnout Vandecappelle <arnout@mind.be>
Cc: Yann E. MORIN <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

Makefile

@@ -294,14 +294,7 @@ unexport TERMINFO
 
 GNU_HOST_NAME:=$(shell support/gnuconfig/config.guess)
 
-################################################################################
-#
-# The list of stuff to build for the target toolchain
-# along with the packages to build for the target.
-#
-################################################################################
-
-TARGETS:= toolchain
+TARGETS :=
 
 # silent mode requested?
 QUIET:=$(if $(findstring s,$(MAKEFLAGS)),-q)

toolchain/Config.in

@@ -1,5 +1,11 @@
 menu "Toolchain"
 
+# Invisible option that makes sure the toolchain package always gets
+# built
+config BR2_TOOLCHAIN
+	bool
+	default y
+
 # Should be selected for glibc or eglibc
 config BR2_TOOLCHAIN_USES_GLIBC
 	bool