[PATCH 2/3] tools build: Fix Makefile(s) to properly invoke tools build

Several fixes were needed to allow following builds: $ make tools/tmon $ make -C tools/perf $ make -C /tools perf - some of the tools (perf) use same make variables as in kernel build, unsetting srctree and objtree - using original $(O) for O variable - perf build does not follow the

[PATCH 2/3] tools build: Fix Makefile(s) to properly invoke tools build

Several fixes were needed to allow following builds: $ make tools/tmon $ make -C kernelsrc tools/perf $ make -C kernelsrc/tools perf - some of the tools (perf) use same make variables as in kernel build, unsetting srctree and objtree - using original $(O) for O variable - perf build