Update RG350 defconfig

I've recently done some massive updates to the buildroot, necessitating
some minor changes to the defconfig here.

Good news: The buildroot use GCC 5.4 and newer binutils, so it now
builds with LTO.

Packaging/OpenDingux/rg350_devilutionx_defconfig

@@ -3,11 +3,12 @@ BR2_mips_xburst=y
 # BR2_MIPS_SOFT_FLOAT is not set
 BR2_OPTIMIZE_2=y
 BR2_KERNEL_HEADERS_3_12=y
+BR2_UCLIBC_CONFIG="board/opendingux/gcw0/uclibc.config"
 BR2_TOOLCHAIN_BUILDROOT_LARGEFILE=y
 BR2_TOOLCHAIN_BUILDROOT_INET_IPV6=y
 BR2_TOOLCHAIN_BUILDROOT_WCHAR=y
 BR2_BINUTILS_EXTRA_CONFIG_OPTIONS="--enable-lto"
-BR2_GCC_VERSION_4_9_X=y
+BR2_GCC_VERSION_5_X=y
 BR2_EXTRA_GCC_CONFIG_OPTIONS="--enable-lto"
 BR2_TOOLCHAIN_BUILDROOT_CXX=y
 BR2_PACKAGE_SDL=y