POWER9 platforms switch to GCC6

Fixes: https://github.com/open-power/op-build/issues/755
Signed-off-by: Stewart Smith <stewart@linux.vnet.ibm.com>
diff --git a/openpower/configs/p9dsu_defconfig b/openpower/configs/p9dsu_defconfig
index bebfbcd..d72fc70 100644
--- a/openpower/configs/p9dsu_defconfig
+++ b/openpower/configs/p9dsu_defconfig
@@ -3,7 +3,7 @@
 BR2_GLIBC_VERSION_2_25=y
 BR2_BINUTILS_VERSION_2_28_X=y
 BR2_BINUTILS_EXTRA_CONFIG_OPTIONS="--enable-targets=powerpc64-linux"
-BR2_GCC_VERSION_4_9_X=y
+BR2_GCC_VERSION_6_X=y
 BR2_EXTRA_GCC_CONFIG_OPTIONS="--enable-targets=powerpc64-linux"
 BR2_TOOLCHAIN_BUILDROOT_CXX=y
 BR2_TARGET_GENERIC_HOSTNAME="skiroot"