libblocksruntime depends on clang to build and Debian clang package
current provides clang 3.8, however clang 3.8 has a bug  when using
-fstack-protector to link on ppc64le.
This bug was fixed by commits r265851, r266806 and r266809 and are
part of clang 3.9. I tested and with clang 3.9 libblocksruntime
package builds fine on ppc64le.
Said that, to solve this bug we can use one of the approaches bellow:
1) Upgrade Debian clang package to point to clang-3.9
2) Backport patches that fixes this issue to Debian clang-3.8 package.
 - https://bugs.llvm.org/show_bug.cgi?id=26226