toolchain-external: support more gdbserver locations

The x86/x86-64 CodeSourcery toolchains use some weird locations for
the gdbserver binary:

$ find . -name 'gdbserver'
./i686-pc-linux-gnu/libc/atom/usr/bin/gdbserver
./i686-pc-linux-gnu/libc/atom/usr/lib/bin/gdbserver
./i686-pc-linux-gnu/libc/core2/usr/bin/gdbserver
./i686-pc-linux-gnu/libc/core2/usr/lib64/bin/gdbserver
./i686-pc-linux-gnu/libc/usr/lib/bin/gdbserver
./i686-pc-linux-gnu/libc/usr/lib64/bin/gdbserver

Notice that it's sometimes hidden in a usr/{lib,lib64}/bin
directory. This patch changes the gdbserver logic to also try in this
location.

Originally based on work done by Daniel Nilsson, visible at
http://patchwork.ozlabs.org/patch/155767/.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

toolchain/toolchain-external/ext-tool.mk

@@ -444,9 +444,9 @@ $(STAMP_DIR)/ext-toolchain-installed: $(STAMP_DIR)/ext-toolchain-checked
 	if test x"$(BR2_TOOLCHAIN_EXTERNAL_GDB_SERVER_COPY)" == x"y"; then \
 		$(call MESSAGE,"Copying gdbserver") ; \
 		gdbserver_found=0 ; \
-		for d in $${ARCH_SYSROOT_DIR} $${ARCH_SYSROOT_DIR}/../debug-root/ ; do \
-			if test -f $${d}/usr/bin/gdbserver ; then \
-				install -m 0755 -D $${d}/usr/bin/gdbserver $(TARGET_DIR)/usr/bin/gdbserver ; \
+		for d in $${ARCH_SYSROOT_DIR}/usr $${ARCH_SYSROOT_DIR}/../debug-root/usr $${ARCH_SYSROOT_DIR}/usr/$${ARCH_LIB_DIR} ; do \
+			if test -f $${d}/bin/gdbserver ; then \
+				install -m 0755 -D $${d}/bin/gdbserver $(TARGET_DIR)/usr/bin/gdbserver ; \
 				gdbserver_found=1 ; \
 				break ; \
 			fi ; \