Revert "Update llvm to 714a9d742af9ce911a3a46aa6e55041099a04be1."

This reverts commit 6f00d9e697266483ea3a6b10191f2e82783af62d.

Revert this, the bots fail with:

configure: error:
The selected GCC C++ compiler is not new enough to build LLVM. Please upgrade
to GCC 4.7. You may pass --disable-compiler-version-checks to configure to
bypass these sanity checks.