perf bpf: Fix build breakage due to libbpf

perf build is currently (v4.4-rc5) broken on powerpc:

bpf.c:28:4: error: #error __NR_bpf not defined. libbpf does not support
your arch.
# error __NR_bpf not defined. libbpf does not support your arch.
^

Fix this by including tools/scripts/Makefile.arch for the proper $ARCH
macro. While at it, remove redundant LP64 macro definition.

Also, since libbpf require $(srctree) now, detect the path of srctree
like perf.

Signed-off-by: Naveen N. Rao <[e-mail]>
Acked-by: Jiri Olsa <[e-mail]>
Cc: Sukadev Bhattiprolu <[e-mail]>
Cc: Wang Nan <[e-mail]>
Cc: Zefan Li <[e-mail]>
Cc: [e-mail]
Link: http://lkml.kernel.org/r/[e-mail]
[Use tools/scripts/Makefile.arch]
Signed-off-by: Wang Nan <[e-mail]>
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/lib/bpf/Makefile

···
 
 MAKEFLAGS += --no-print-directory
 
+ifeq ($(srctree),)
+srctree := $(patsubst %/,%,$(dir $(shell pwd)))
+srctree := $(patsubst %/,%,$(dir $(srctree)))
+srctree := $(patsubst %/,%,$(dir $(srctree)))
+#$(info Determined 'srctree' to be $(srctree))
+endif
 
 # Makefiles suck: This macro sets a default value of $(2) for the
 # variable named by $(1), unless the variable has been set by
···
 DESTDIR ?=
 DESTDIR_SQ = '$(subst ','\'',$(DESTDIR))'
 
-LP64 := $(shell echo __LP64__ | ${CC} ${CFLAGS} -E -x c - | tail -n 1)
+include $(srctree)/tools/scripts/Makefile.arch
+
 ifeq ($(LP64), 1)
   libdir_relative = lib64
 else
···
 endif
 ifndef VERBOSE
   VERBOSE = 0
-endif
-
-ifeq ($(srctree),)
-srctree := $(patsubst %/,%,$(dir $(shell pwd)))
-srctree := $(patsubst %/,%,$(dir $(srctree)))
-srctree := $(patsubst %/,%,$(dir $(srctree)))
-#$(info Determined 'srctree' to be $(srctree))
 endif
 
 FEATURE_USER = .libbpf