Create virtual packages for OpenPower toolchain

Create a "toolchain" category, plus "p8-pore-toolchain" and
"ppe42-toolchain" virtual-packages, with the goal of lowering the
coupling between these toolchain and target packages.

Signed-off-by: Klaus Heinrich Kiwi <klaus@linux.vnet.ibm.com>
diff --git a/openpower/package/ppe42-gcc/ppe42-gcc.mk b/openpower/package/ppe42-gcc/ppe42-gcc.mk
index 518e458..a59071d 100644
--- a/openpower/package/ppe42-gcc/ppe42-gcc.mk
+++ b/openpower/package/ppe42-gcc/ppe42-gcc.mk
@@ -10,6 +10,7 @@
 
 PPE42_GCC_DEPENDENCIES = ppe42-binutils gmp mpfr mpc
 HOST_PPE42_GCC_DEPENDENCIES = host-ppe42-binutils host-gmp host-mpfr host-mpc
+PPE42_GCC_PROVIDES = ppe42-toolchain
 
 PPE42_GCC_DIR = $(STAGING_DIR)/ppe42-binutils
 PPE42_GCC_BIN = $(STAGING_DIR)/ppe42-binutils/linux