Add LLDB in release binaries by default

LLDB is currently not selected in LLVM release testing and thus it
doesnt make its way into prebuilt binaries which build with default
configuration. This patch enables LLDB by default in test-release
script.

Assuming LLDB build by default was disabled back in 2016 LLDB support
for various architectures has a long way since then. It has buildbots
for most architectures and supports a case to be included by default.

Also lldb build can easily be disabled in case some release managers
choose to do so.

Reviewed By: tstellar

Differential Revision: https://reviews.llvm.org/D101864