[CMake] Make it possible to set the RPATH in add_lldb_exectable.
[CMake] Make it possible to set the RPATH in add_lldb_exectable.

Make it possible to pass a build and install RPATH to
add_lldb_executable instead of having to call lldb_setup_rpaths after
the fact.

This fixes a real issue where setting an install RPATH with
lldb_setup_rpaths would only affect the symroot installation component.
Given that lldb_setup_rpaths sets a target property I would expect this
to be orthogonal to installation components. Regardless, it makes sense
to integrate this functionality in add_lldb_exectable.

git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@375068 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit 0f53352cb22da3e0bd5e4d4272e9849e9883f11e)

apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb