If someone specifies a single target, mixed with O=, the following way:

    hubble:~/tip/tools/perf> make O=/tmp/perf util/stat.o
    BUILD: Doing 'make -j8' parallel build
    gcc  -Wbad-function-cast -Wdeclaration-after-statement -Wformat-security -Wformat-y2k [...]

The build might even fail, if a target depends on other targets:

    hubble:~/tip/tools/perf> make O=/tmp/perf perf.o
    ...
    perf.c: In function ‘handle_options’:
    perf.c:155:21: error: ‘PERF_HTML_PATH’ undeclared (first use in this function)

The correct way to invoke such targets is:

    hubble:~/tip/tools/perf> make O=/tmp/perf /tmp/perf/perf.o
    BUILD: Doing 'make -j8' parallel build
    GEN /tmp/perf/common-cmds.h
    CC /tmp/perf/perf.o

But that's unnecessary typing and it's also easy to mistakenly build into the
source directory.

To fix this remove the generic suffix rules and add redirection to $(OUTPUT)
for the most popular .o targets.

Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lkml.kernel.org/n/tip-mk0oiukmhgSbrll6chrPkkqr@git.kernel.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>