toolchain/toolchain-buildroot: migrate to virtual package infrastructure

This patch migrates the toolchain and toolchain-buildroot packages to the
virtual package infrastructure, causing the log messages to change from:

>>> toolchain undefined Downloading
>>> toolchain undefined Extracting
...

to

>>> toolchain virtual Downloading
>>> toolchain virtual Extracting
...

and similar for 'toolchain-buildroot', simply because it looks nicer.

At the same time, the directory names also become toolchain-virtual,
toolchain-buildroot-virtual instead of the corresponding 'undefined'
variants.

Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

toolchain/toolchain-buildroot/toolchain-buildroot.mk

@@ -4,8 +4,6 @@
 #
 ################################################################################
 
-TOOLCHAIN_BUILDROOT_SOURCE =
-
 BR_LIBC = $(call qstrip,$(BR2_TOOLCHAIN_BUILDROOT_LIBC))
 
 # Triggering the build of the host-gcc-final will automatically do the
@@ -16,4 +14,4 @@ TOOLCHAIN_BUILDROOT_DEPENDENCIES = host-gcc-final
 
 TOOLCHAIN_BUILDROOT_ADD_TOOLCHAIN_DEPENDENCY = NO
 
-$(eval $(generic-package))
+$(eval $(virtual-package))

toolchain/toolchain/toolchain.mk

@@ -4,8 +4,6 @@
 #
 ################################################################################
 
-TOOLCHAIN_SOURCE =
-
 ifeq ($(BR2_TOOLCHAIN_BUILDROOT),y)
 TOOLCHAIN_DEPENDENCIES += toolchain-buildroot
 else ifeq ($(BR2_TOOLCHAIN_EXTERNAL),y)
@@ -14,6 +12,6 @@ endif
 
 TOOLCHAIN_ADD_TOOLCHAIN_DEPENDENCY = NO
 
-$(eval $(generic-package))
+$(eval $(virtual-package))
 
 toolchain: $(HOST_DIR)/usr/share/buildroot/toolchainfile.cmake