package/libmemcached: fix static build

Fix the following static build failure raised since bump to version
1.1.4 in commit 7205df8a4f3c729b11a5f0c34885e6cf592f24b9:

CMake Error at /home/autobuild/autobuild/instance-13/output-1/build/libmemcached-1.1.4/src/bin/cmake_install.cmake:60 (file):
  file RPATH_CHANGE could not write new RPATH:

    $ORIGIN/../lib

  to the file:

    /home/autobuild/autobuild/instance-13/output-1/host/arc-buildroot-linux-uclibc/sysroot/usr/bin/memcapable

  No valid ELF RPATH or RUNPATH entry exists in the file;
Call Stack (most recent call first):
  /home/autobuild/autobuild/instance-13/output-1/build/libmemcached-1.1.4/src/cmake_install.cmake:52 (include)
  /home/autobuild/autobuild/instance-13/output-1/build/libmemcached-1.1.4/cmake_install.cmake:52 (include)

Fixes:
 - http://autobuild.buildroot.org/results/778ff517d465896f54a3cd5316a66c54f66fd4cb

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
(cherry picked from commit b47b2065b249b3f50f3164d8a8114b108f596559)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/libmemcached/libmemcached.mk

@@ -18,7 +18,8 @@ LIBMEMCACHED_CPE_ID_VENDOR = awesome
 # unexpected build failures with packages that use libmemcached (e.g. c-icap)
 LIBMEMCACHED_CONF_OPTS += \
 	-DCMAKE_BUILD_TYPE=Release \
-	-DCMAKE_C_FLAGS="$(TARGET_CFLAGS) -std=c99"
+	-DCMAKE_C_FLAGS="$(TARGET_CFLAGS) -std=c99" \
+	-DCMAKE_SKIP_RPATH=ON
 
 ifeq ($(BR2_PACKAGE_LIBEVENT),y)
 LIBMEMCACHED_DEPENDENCIES += libevent