[lldb-dev] Optional Dependencies in LLDB

[Jonas Devlieghere via lldb-dev]

Hey everyone,

I just wanted to let you know that most of the work is complete for
auto-detecting optional dependencies in LLDB. Unless explicitly
specified, optional dependencies like editline will be enabled when
available and disabled otherwise. This is different from  the old
behavior, where optional dependencies were that were enabled by
default would cause an error at configuration time. The motivation is
to make it easier to build LLDB by making things "just work" out of
the box.

All optional dependencies are now controlled by an LLDB_ENABLE_* CMake
flag. The default value for these variables is "Auto", which causes
the dependency to be enabled based on whether it was found. It's still
possible to obtain the old behavior by setting the corresponding CMake
variable to "On" or "Off" respectively.

If you have a configuration where you were depending on the old
behavior where the dependency being enabled or disabled by default,
you might want to consider passing LLDB_ENABLE_*=On/Off to CMake to
ensure the dependency is required or ignored respectively.

TL;DR Optional dependencies in LLDB are controlled by LLDB_ENABLE_*
CMake flags and are auto-detected by default. You can return to the
old behavior by setting the variables to "On" or "Off" respectively.