perf build: Don't propagate subdir to submakes for install_headers

subdir is added to the OUTPUT which fails as part of building
install_headers when passed from "make -C tools perf_install".

Committer testing:

The original reporter (see the Link: below) had trouble with this:

$ make -C tools perf_install

That ended up with errors like this:

  /var/home/acme/git/perf-urgent/tools/scripts/Makefile.include:17: *** output directory "/var/home/acme/git/perf-urgent/tools/perf/libperf/perf/" does not exist.  Stop.

With this patch applied we now get it installed at:

  INSTALL /var/home/acme/git/perf-urgent/tools/perf/libperf/include/perf/bpf_perf.h

As expected:

  $ ls -la /var/home/acme/git/perf-urgent/tools/perf/libperf/include/perf/bpf_perf.h
  -rw-r--r--. 1 acme acme 1146 Jan  3 15:42 /var/home/acme/git/perf-urgent/tools/perf/libperf/include/perf/bpf_perf.h

And if we clean tools with:

  $ make -C tools clean

it gets cleaned up:

  $ ls -la /var/home/acme/git/perf-urgent/tools/perf/libperf/include/perf/bpf_perf.h
  ls: cannot access '/var/home/acme/git/perf-urgent/tools/perf/libperf/include/perf/bpf_perf.h': No such file or directory
  $

Fixes: 746bd29e ("perf build: Use tools/lib headers from install path")
Reported-by: Torsten Hilbrich <torsten.hilbrich@secunet.com>
Signed-off-by: Ian Rogers <irogers@google.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/fa4b3115-d555-3d7f-54d1-018002e99350@secunet.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Makefile.perf

@@ -819,7 +819,7 @@ $(patsubst perf-%,%.o,$(PROGRAMS)): $(wildcard */*.h)
 
 $(LIBAPI): FORCE | $(LIBAPI_OUTPUT)
 	$(Q)$(MAKE) -C $(LIBAPI_DIR) O=$(LIBAPI_OUTPUT) \
-		DESTDIR=$(LIBAPI_DESTDIR) prefix= \
+		DESTDIR=$(LIBAPI_DESTDIR) prefix= subdir= \
 		$@ install_headers
 
 $(LIBAPI)-clean:
@@ -828,7 +828,7 @@ $(LIBAPI)-clean:
 
 $(LIBBPF): FORCE | $(LIBBPF_OUTPUT)
 	$(Q)$(MAKE) -C $(LIBBPF_DIR) FEATURES_DUMP=$(FEATURE_DUMP_EXPORT) \
-		O= OUTPUT=$(LIBBPF_OUTPUT)/ DESTDIR=$(LIBBPF_DESTDIR) prefix= \
+		O= OUTPUT=$(LIBBPF_OUTPUT)/ DESTDIR=$(LIBBPF_DESTDIR) prefix= subdir= \
 		$@ install_headers
 
 $(LIBBPF)-clean:
@@ -837,7 +837,7 @@ $(LIBBPF)-clean:
 
 $(LIBPERF): FORCE | $(LIBPERF_OUTPUT)
 	$(Q)$(MAKE) -C $(LIBPERF_DIR) O=$(LIBPERF_OUTPUT) \
-		DESTDIR=$(LIBPERF_DESTDIR) prefix= \
+		DESTDIR=$(LIBPERF_DESTDIR) prefix= subdir= \
 		$@ install_headers
 
 $(LIBPERF)-clean:
@@ -846,7 +846,7 @@ $(LIBPERF)-clean:
 
 $(LIBSUBCMD): FORCE | $(LIBSUBCMD_OUTPUT)
 	$(Q)$(MAKE) -C $(LIBSUBCMD_DIR) O=$(LIBSUBCMD_OUTPUT) \
-		DESTDIR=$(LIBSUBCMD_DESTDIR) prefix= \
+		DESTDIR=$(LIBSUBCMD_DESTDIR) prefix= subdir= \
 		$@ install_headers
 
 $(LIBSUBCMD)-clean:
@@ -855,7 +855,7 @@ $(LIBSUBCMD)-clean:
 
 $(LIBSYMBOL): FORCE | $(LIBSYMBOL_OUTPUT)
 	$(Q)$(MAKE) -C $(LIBSYMBOL_DIR) O=$(LIBSYMBOL_OUTPUT) \
-		DESTDIR=$(LIBSYMBOL_DESTDIR) prefix= \
+		DESTDIR=$(LIBSYMBOL_DESTDIR) prefix= subdir= \
 		$@ install_headers
 
 $(LIBSYMBOL)-clean: