build: make rpath optional

Type: feature

This patch begins enabling support for building VPP as a package for a
Yocto-based embedded Linux distribution. Yocto QA complains about
executables and libraries with an rpath configured, as the paths may not
be valid on the target system. Therefore, this patch adds a new CMake
option named `VPP_SET_RPATH`, which is enabled by default but can be
disabled by a Yocto-based build.

Change-Id: I90e9c4ba07138032b0f76cb72a98e58470885d55
Signed-off-by: Nathan Moos <nmoos@cisco.com>
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 8947c8a..15e0673 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -136,7 +136,10 @@
 ##############################################################################
 # install config
 ##############################################################################
-set(CMAKE_INSTALL_RPATH "${CMAKE_INSTALL_PREFIX}/lib")
+option(VPP_SET_RPATH "Set rpath for resulting binaries and libraries." ON)
+if(VPP_SET_RPATH)
+  set(CMAKE_INSTALL_RPATH "${CMAKE_INSTALL_PREFIX}/lib")
+endif()
 set(CMAKE_INSTALL_MESSAGE NEVER)
 
 include_directories (