Modifications to update.py: * The script now clones and builds llvm in a temporary location based on the LLVM_BRANCH and LLVM_COMMIT variables in the script. * Added logging, including for execution of commands * Now setting LLVM_ENABLE_THREADS=ON as we recently manually enabled multithreading for the LLVM backend. Change-Id: I53bed46d890c0da234c4245d456c83280bf7b370 Bug: b/152339534 Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/46188Reviewed-by: Nicolas Capens <nicolascapens@google.com> Kokoro-Result: kokoro <noreply+kokoro@google.com> Tested-by: Antonio Maiorano <amaiorano@google.com>