Update LLVM_PREBUILT_VERSION to clang-r346389 am: 371c0435b7 am: d939074be7
am: a2b68bbe90

Change-Id: I65c3163422ac80723dcdc5c7b131bc4cabf5fba4
tree: b369903bc8be116f2e896b365aeba53308f754a2
  1. darwin-x86/
  2. linux-x86/
  3. build-prebuilts.sh
  4. manifest.xml