Change libLTO back to linking with @executable_path instead of @rpath.

This partially reverts r187641 until ld64 adopts a change to link with an
rpath setting.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194418 91177308-0d34-0410-b5e6-96231b3b80d8

tools/lto/Makefile

@@ -46,7 +46,7 @@ ifeq ($(HOST_OS),Darwin)
     ifneq ($(DARWIN_VERS),8)
        LLVMLibsOptions    := $(LLVMLibsOptions)  \
                             -Wl,-install_name \
-                            -Wl,"@rpath/lib$(LIBRARYNAME)$(SHLIBEXT)"
+                            -Wl,"@executable_path/../lib/lib$(LIBRARYNAME)$(SHLIBEXT)"
     endif
 
     # If we're doing an Apple-style build, add the LTO object path.