Revert "Revert "Use relative rpath so that the installation and build dirs are relocatable.""

This reverts commit r201934.

Polly has been fixed to work with this.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@201936 91177308-0d34-0410-b5e6-96231b3b80d8

CMakeLists.txt

@@ -423,9 +423,13 @@ set( CMAKE_RUNTIME_OUTPUT_DIRECTORY ${LLVM_BINARY_DIR}/bin )
 set( CMAKE_LIBRARY_OUTPUT_DIRECTORY ${LLVM_BINARY_DIR}/lib )
 set( CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${LLVM_BINARY_DIR}/lib )
 
-if( NOT DEFINED CMAKE_INSTALL_RPATH )
-  set( CMAKE_INSTALL_RPATH "\$ORIGIN/../lib")
-endif( NOT DEFINED CMAKE_INSTALL_RPATH )
+set(CMAKE_BUILD_WITH_INSTALL_RPATH ON)
+if (APPLE)
+  set(CMAKE_INSTALL_NAME_DIR "@rpath")
+  set(CMAKE_INSTALL_RPATH "@executable_path/../lib")
+else(UNIX)
+  set(CMAKE_INSTALL_RPATH "\$ORIGIN/../lib")
+endif()
 
 set(CMAKE_INCLUDE_CURRENT_DIR ON)