Always use prebuilt clang, even if we're explicitly building clang/LLVM.

This is needed for self-hosting Clang/LLVM.

bug 13588226

Change-Id: Ic98adc2b174b12ce046b7b65bbc28901a766a485
Merge "Always use prebuilt clang, even if we're explicitly building clang/LLVM."
Remove redundant my_target_global_ldflags

  * Fix: my_target_global_ldflags is defined in binary.mk
    so they effectivelly override previous definition

Change-Id: I9c7d9bde82c3a6d25a94ae109fa71ecaa33640b0
Merge "Remove redundant my_target_global_ldflags"
auto-merger: merge in from aosp/master