lldb: don't build rpaths into binaries

lldb: don't build rpaths into binaries

LLDB defaults to adding rpaths into the binaries which are then stripped
by CMake on install.

However, this rpath removal is implemented by editing the binary instead
of relinking at install time, so the final binary will have an entry in
the dynstr section which is all nulls but is as long as the build path.

Obviously this breaks reproducibility, so disable the use of rpaths in
LLDB to remove this problem.

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>