perf currently fails to build on MIPS as there is no
tools/perf/arch/mips/Build file. Adding an empty file fixes this as
there are no MIPS-specific sources to build.
It looks like the same is needed for Alpha and PA-RISC, though I
haven't been able to test those.
Signed-off-by: Ben Hutchings <email@example.com>
Fixes: 5e8c0fb6a957 ("perf build: Add arch x86 objects building")
Cc: Peter Zijlstra <firstname.lastname@example.org>
Signed-off-by: Arnaldo Carvalho de Melo <email@example.com>