toolchain: detect external glibc in merged /usr

When using an external toolchain that was built with Buildroot and a
merged /usr, the dynamic linker is actually in /usr/lib.

But the check_glibc macro limits the depth it is looking for the dynamic
linker, and misses it when it is in /usr/lib because it is too deep.

We could fix that in two ways: increase the depth in which we look
for it, or follow symlinks. We choose the second solution.

Signed-off-by: Cam Hutchison <camh@xdna.net>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Thomas De Schampheleire <thomas.de_schampheleire@nokia.com>
Cc: "Yann E. MORIN" <yann.morin.1998@free.fr>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
(cherry picked from commit b55ff5a7cdaa8a45101d11a3c095d9aeab1f0ce4)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

toolchain/helpers.mk

@@ -227,7 +227,7 @@ check_glibc_rpc_feature = \
 #
 check_glibc = \
 	SYSROOT_DIR="$(strip $1)"; \
-	if test `find $${SYSROOT_DIR}/ -maxdepth 2 -name 'ld-linux*.so.*' -o -name 'ld.so.*' -o -name 'ld64.so.*' | wc -l` -eq 0 ; then \
+	if test `find -L $${SYSROOT_DIR}/ -maxdepth 2 -name 'ld-linux*.so.*' -o -name 'ld.so.*' -o -name 'ld64.so.*' | wc -l` -eq 0 ; then \
 		echo "Incorrect selection of the C library"; \
 		exit -1; \
 	fi; \