perf test: Add Build file to dependencies for llvm-src-*.c

Because the Build file writes source code to the generated llvm-src-*.c
files, it should be listed as one of the dependencies, so that any
future changes to the code being echoed won't require a 'make clean'.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/9b9886c295750dc83cbbb29a665d280f9c5e8b3e.1449965119.git.jpoimboe@redhat.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>