llvm_tools: parameterize update_chromeos_llvm_next_hash.py

Currently update_chromeos_llvm_next_hash.py can only be used to create
CLs that update LLVM_NEXT_HASH in toolchain-related ebuild files, as it
hardcoded which git hash to update. This change allows users to choose
betwen LLVM_HASH and LLVM_NEXT_HASH, and therefore can be used to create
LLVM roll CLs automatically.

BUG=chromium:1057428

TEST=local tests

Change-Id: Ifc0cadb7b618d4780aceb92dcc8891941c612ecb
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/toolchain-utils/+/2112250
Reviewed-by: Bob Haarman <inglorion@chromium.org>
Reviewed-by: Manoj Gupta <manojgupta@chromium.org>
Tested-by: Jian Cai <jiancai@google.com>
4 files changed