perf test: Add test cases for new data source encoding

Add some simple tests to perf test to test data source printing.

v2: Make the tests actually checked for the correct name of Forward
v3: Adjust to new encoding

Committer notes:

Avoid the in place declaration to make this build with older compilers,
for instance, in Debian 7 we get:

  tests/mem.c: In function 'test__mem':
  tests/mem.c:30:5: error: missing initializer [-Werror=missing-field-initializers]
  tests/mem.c:30:5: error: (near initialization for '(anonymous).<anonymous>.mem_snoop') [-Werror=missing-field-initializers]

So just zero a struct, then go on building the unions as needed,
reusing settings from the previous test, i.e. local -> remote, etc.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Link: http://lkml.kernel.org/r/20170816222156.19953-5-andi@firstfloor.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/Build

@@ -34,6 +34,7 @@ perf-y += thread-map.o
 perf-y += llvm.o llvm-src-base.o llvm-src-kbuild.o llvm-src-prologue.o llvm-src-relocation.o
 perf-y += bpf.o
 perf-y += topology.o
+perf-y += mem.o
 perf-y += cpumap.o
 perf-y += stat.o
 perf-y += event_update.o