toolchain/toolchain-buildroot: add comment about using virtual packag…

…e infra

Commit "9a8ec9195c toolchain/toolchain-buildroot: migrate to virtual
package infrastructure" made the packages toolchain and
toolchain-buildroot to use the virtual package infra even they being
generic packages.
This works because on package/pkg-virtual.mk when a package do not
define neither _PROVIDES_ or _HAS_ symbols, only _IS_VIRTUAL is set to
YES and _VERSION and _SOURCE are set to empty before relaying the call
to inner-generic-package.

Add a comment explaining why the virtual package infra is used in these
cases.

Cc: Giulio Benetti <[email protected]>
Cc: Romain Naour <[email protected]>
Cc: Thomas De Schampheleire <[email protected]>
Cc: Thomas Petazzoni <[email protected]>
Cc: Yann E. MORIN <[email protected]>
Signed-off-by: Ricardo Martincoski <[email protected]>
Signed-off-by: Peter Korsgaard <[email protected]>

toolchain/toolchain-buildroot/toolchain-buildroot.mk

@@ -14,4 +14,7 @@ TOOLCHAIN_BUILDROOT_DEPENDENCIES = host-gcc-final
 
 TOOLCHAIN_BUILDROOT_ADD_TOOLCHAIN_DEPENDENCY = NO
 
+# Not really a virtual package, but we use the virtual package infra here so
+# both the build log and build directory look nicer (toolchain-buildroot-virtual
+# instead of toolchain-buildroot-undefined)
 $(eval $(virtual-package))

toolchain/toolchain/toolchain.mk

@@ -47,4 +47,7 @@ endef
 TOOLCHAIN_POST_INSTALL_TARGET_HOOKS += TOOLCHAIN_GLIBC_COPY_NSSWITCH_FILE
 endif
 
+# Not really a virtual package, but we use the virtual package infra here so
+# both the build log and build directory look nicer (toolchain-virtual instead
+# of toolchain-undefined)
 $(eval $(virtual-package))