tools: Let O= makes handle a relative path with -C option

When I tried to compile tools/perf from the top directory with the -C
option, the O= option didn't work correctly if I passed a relative path:

  $ make O=BUILD -C tools/perf/
  make: Entering directory '/home/mhiramat/ksrc/linux/tools/perf'
    BUILD:   Doing 'make -j8' parallel build
  ../scripts/Makefile.include:4: *** O=/home/mhiramat/ksrc/linux/tools/perf/BUILD does not exist.  Stop.
  make: *** [Makefile:70: all] Error 2
  make: Leaving directory '/home/mhiramat/ksrc/linux/tools/perf'

The O= directory existence check failed because the check script ran in
the build target directory instead of the directory where I ran the make
command.

To fix that, once change directory to $(PWD) and check O= directory,
since the PWD is set to where the make command runs.

Fixes: c883122a ("perf tools: Let O= makes handle relative paths")
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Michal Marek <michal.lkml@markovi.net>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sasha Levin <sashal@kernel.org>
Cc: Steven Rostedt (VMware) <rostedt@goodmis.org>
Cc: stable@vger.kernel.org
Link: http://lore.kernel.org/lkml/158351957799.3363.15269768530697526765.stgit@devnote2Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Makefile

@@ -35,7 +35,7 @@ endif
 # Only pass canonical directory names as the output directory:
 #
 ifneq ($(O),)
-  FULL_O := $(shell readlink -f $(O) || echo $(O))
+  FULL_O := $(shell cd $(PWD); readlink -f $(O) || echo $(O))
 endif
 
 #

tools/scripts/Makefile.include

 # SPDX-License-Identifier: GPL-2.0
 ifneq ($(O),)
 ifeq ($(origin O), command line)
-	dummy := $(if $(shell test -d $(O) || echo $(O)),$(error O=$(O) does not exist),)
-	ABSOLUTE_O := $(shell cd $(O) ; pwd)
+	dummy := $(if $(shell cd $(PWD); test -d $(O) || echo $(O)),$(error O=$(O) does not exist),)
+	ABSOLUTE_O := $(shell cd $(PWD); cd $(O) ; pwd)
 	OUTPUT := $(ABSOLUTE_O)/$(if $(subdir),$(subdir)/)
 	COMMAND_O := O=$(ABSOLUTE_O)
 ifeq ($(objtree),)