build: Don't fail if SWIG isn't found
build: Don't fail if SWIG isn't found

People from distros have reported that packaging the newer versions is
more difficult because we now depend on SWIG. We don't have to, it's
needed for the python dumper and is an optional build dependency.

Signed-off-by: Damien Lespiau <64bd3cb94f359c1a3ce68dae5e26b40578526277@intel.com>
Signed-off-by: Daniel Vetter <c1b6782c4af8f0673da8923a0702a1832e5940f4@ffwll.ch>

chenxianqin/intel-gpu-tools,tiagovignatti/intel-gpu-tools,dlespiau/checkmate-test-igt,tiagovignatti/intel-gpu-tools,mv0/intel-gpu-tools,dlespiau/checkmate-test-igt,chenxianqin/intel-gpu-tools,yipdw/intel-gpu-tools,erikarn/intel-gpu-tools,mv0/intel-gpu-tools,yipdw/intel-gpu-tools,erikarn/intel-gpu-tools,mv0/intel-gpu-tools,chenxianqin/intel-gpu-tools,chenxianqin/intel-gpu-tools,tiagovignatti/intel-gpu-tools,erikarn/intel-gpu-tools,tiagovignatti/intel-gpu-tools,dlespiau/checkmate-test-igt,mv0/intel-gpu-tools,erikarn/intel-gpu-tools,yipdw/intel-gpu-tools,dlespiau/checkmate-test-igt,yipdw/intel-gpu-tools