Instead of patching the python module detection, we can use the hidden
option LLVM_TOOL_OPT_VIEWER_BUILD.
(From OE-Core rev: ddbbd49c15bad1b2a550188581ffebd752b9b20e)
Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>