toolchain-external: fix installation for CodeSourcery AArch64 toolchain

The extracted toolchain sources contains a single symlink in the
aarch64-linux-gnu/libc/lib directory wich is lost during Buildroot's
staging install.

aarch64-linux-gnu/libc/lib/ld-linux-aarch64.so.1 -> ../lib64/ld-2.18.so

Add a custom post install staging and target hooks to create it
manually.

Signed-off-by: Romain Naour <romain.naour@openwide.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
[Thomas: also make the same tweak in the target.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

toolchain/toolchain-external/toolchain-external.mk

@@ -383,6 +383,14 @@ endif
 else ifeq ($(BR2_TOOLCHAIN_EXTERNAL_CODESOURCERY_AARCH64),y)
 TOOLCHAIN_EXTERNAL_SITE = http://sourcery.mentor.com/public/gnu_toolchain/aarch64-linux-gnu
 TOOLCHAIN_EXTERNAL_SOURCE = aarch64-2014.05-30-aarch64-linux-gnu-i686-pc-linux-gnu.tar.bz2
+define TOOLCHAIN_EXTERNAL_CODESOURCERY_AARCH64_STAGING_FIXUP
+	ln -sf ld-2.18.so $(STAGING_DIR)/lib/ld-linux-aarch64.so.1
+endef
+TOOLCHAIN_EXTERNAL_POST_INSTALL_STAGING_HOOKS += TOOLCHAIN_EXTERNAL_CODESOURCERY_AARCH64_STAGING_FIXUP
+define TOOLCHAIN_EXTERNAL_CODESOURCERY_AARCH64_TARGET_FIXUP
+	ln -sf ld-2.18.so $(TARGET_DIR)/lib/ld-linux-aarch64.so.1
+endef
+TOOLCHAIN_EXTERNAL_POST_INSTALL_STAGING_HOOKS += TOOLCHAIN_EXTERNAL_CODESOURCERY_AARCH64_TARGET_FIXUP
 else ifeq ($(BR2_TOOLCHAIN_EXTERNAL_MUSL_CROSS),y)
 TOOLCHAIN_EXTERNAL_VERSION = 1.1.12
 TOOLCHAIN_EXTERNAL_SITE = https://googledrive.com/host/0BwnS5DMB0YQ6bDhPZkpOYVFhbk0/musl-$(TOOLCHAIN_EXTERNAL_VERSION)