[llvm] (2 commits) ...Build without -ftree-pre as a workaround for clang segfaulting on x86_64

[Kalev Lember]

Summary of changes:

  8fe0322... undefine PPC on ppc as a temporary workaround for RHBZ#7698 (*)
  9dca0ca... Build without -ftree-pre as a workaround for clang segfault (*)

(*) This commit already existed in another branch; no separate mail sent