[PATCH v4] perf: bpf: Fix build breakage due to libbpf

[Wang Nan]

From: "Naveen N. Rao" <naveen.n.rao at linux.vnet.ibm.com>

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 <naveen.n.rao at linux.vnet.ibm.com>
Signed-off-by: Wang Nan <wangnan0 at huawei.com>
Acked-by: Jiri Olsa <jolsa at kernel.org>
Cc: Arnaldo Carvalho de Melo <acme at kernel.org>
Cc: Sukadev Bhattiprolu <sukadev at linux.vnet.ibm.com>
---

v3 -> v4: Add srctree detector code so directly run 'make' in libbpf
          directory would not cause error.

---
 tools/lib/bpf/Makefile | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/tools/lib/bpf/Makefile b/tools/lib/bpf/Makefile
index 636e3dd..0b6e013 100644
--- a/tools/lib/bpf/Makefile
+++ b/tools/lib/bpf/Makefile
@@ -6,6 +6,12 @@ BPF_EXTRAVERSION = 1
 
 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 $(1), unless the variable has been set by
@@ -31,7 +37,8 @@ INSTALL = install
 DESTDIR ?=
 DESTDIR_SQ = '$(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
-- 
1.8.3.4