tools build: Add detected config support

Adding support to include detected configuration makefile into the build
process. This will allow the Build objects to be configurable based on
the config data, like:

  perf-$(CONFIG_KRAVA) += krava.o

The configuration is stored in '.config-detected' file, which is
generated for each compilation.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Tested-by: Will Deacon <will.deacon@arm.com>
Cc: Alexis Berlemont <alexis.berlemont@gmail.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-bl8qho0ubck7aqrbbfu9inlm@git.kernel.org


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