qemu_v8: Update the EDK2 toolchain

Older EDK2 toolchains (GCC49) will cause errors when updating EDK2, therefore,
we use GCC5 instead.

Signed-off-by: Mingyuan Xiang <xiang_my@outlook.com>
Reviewed-by: Jerome Forissier <jerome@forissier.org>
Tested-by: Jerome Forissier <jerome@forissier.org> (QEMUv8)
diff --git a/qemu_v8.mk b/qemu_v8.mk
index b01a923..87f736c 100644
--- a/qemu_v8.mk
+++ b/qemu_v8.mk
@@ -29,7 +29,7 @@
 TF_A_PATH		?= $(ROOT)/trusted-firmware-a
 BINARIES_PATH		?= $(ROOT)/out/bin
 EDK2_PATH		?= $(ROOT)/edk2
-EDK2_TOOLCHAIN		?= GCC49
+EDK2_TOOLCHAIN		?= GCC5
 EDK2_ARCH		?= AARCH64
 ifeq ($(DEBUG),1)
 EDK2_BUILD		?= DEBUG