perf tools: Speed up build-tests by reducing the number of builds tested

The 'tools/perf/test/make' makefile has in its default, 'all' target
builds that will pollute the source code directory, i.e. that will not
use O= variable.

The 'build-test' should be run as often as possible, preferrably after
each non strictly non-code commit, so speed it up by selecting just
the O= targets.

Furthermore it tests both the Makefile.perf file, that is normally
driven by the main Makefile, and the Makefile, reduce the time in half
by having just MK=Makefile, the most usual, tested by 'build-test'.

Please run:

  make -C tools/perf -f tests/make

from time to time for testing also the in-place build tests.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-jrt9utscsiqkmjy3ccufostd@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Makefile

@@ -75,10 +75,17 @@ clean:
 	$(make)
 
 #
-# The build-test target is not really parallel, don't print the jobs info:
+# The build-test target is not really parallel, don't print the jobs info,
+# it also uses only the tests/make targets that don't pollute the source
+# repository, i.e. that uses O= or builds the tarpkg outside the source
+# repo directories.
+#
+# For a full test, use:
+#
+# make -C tools/perf -f tests/make
 #
 build-test:
-	@$(MAKE) SHUF=1 -f tests/make REUSE_FEATURES_DUMP=1 --no-print-directory
+	@$(MAKE) SHUF=1 -f tests/make REUSE_FEATURES_DUMP=1 MK=Makefile --no-print-directory tarpkg out
 
 #
 # All other targets get passed through: