dlfcn: update ifdef around old_name_

Commit 9185e04f72c16d2a66d92ac89b38ee926d7f706b changed the ifdef around
old_name_ from __arm__ to __work_around_b_###__, but missed one place in
dlfcn.cpp.  So if you do a build w/out that workaround for arm, you end
up with a build failure:
bionic/linker/dlfcn.cpp:275:27: error: no member named 'old_name_' in 'soinfo'
    strlcpy(__libdl_info->old_name_, __libdl_info->soname_, sizeof(__libdl_info->old_name_));
            ~~~~~~~~~~~~  ^
bionic/linker/dlfcn.cpp:275:82: error: no member named 'old_name_' in 'soinfo'
    strlcpy(__libdl_info->old_name_, __libdl_info->soname_, sizeof(__libdl_info->old_name_));
                                                                   ~~~~~~~~~~~~  ^

Bug: 24425865
Change-Id: Idbe1cc1c28083afeee6d90203c221f30f661c69c
diff --git a/linker/dlfcn.cpp b/linker/dlfcn.cpp
index f1b26c9..93189df 100644
--- a/linker/dlfcn.cpp
+++ b/linker/dlfcn.cpp
@@ -271,7 +271,7 @@
     __libdl_info->local_group_root_ = __libdl_info;
     __libdl_info->soname_ = "libdl.so";
     __libdl_info->target_sdk_version_ = __ANDROID_API__;
-#if defined(__arm__)
+#if defined(__work_around_b_24465209__)
     strlcpy(__libdl_info->old_name_, __libdl_info->soname_, sizeof(__libdl_info->old_name_));
 #endif
   }