tools/liblockdep: Use realpath for srctree and objtree

If BUILD_SRC or CURDIR contains tailing '/', the file names passed to gcc will
contain '//'. It will be contained .o's in debuginfo, then confuse debugedit:

https://bugzilla.redhat.com/show_bug.cgi?id=304121

This patch uses realpath command to makesure potential tailing '/'s are removed.
Signed-off-by: Wang Nan <wangnan0@huawei.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Geng Hui <hui.geng@huawei.com>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>

tools/lib/lockdep/Makefile

@@ -87,8 +87,8 @@ endif # BUILD_SRC
 # We process the rest of the Makefile if this is the final invocation of make
 ifeq ($(skip-makefile),)
 
-srctree		:= $(if $(BUILD_SRC),$(BUILD_SRC),$(CURDIR))
-objtree		:= $(CURDIR)
+srctree		:= $(realpath $(if $(BUILD_SRC),$(BUILD_SRC),$(CURDIR)))
+objtree		:= $(realpath $(CURDIR))
 src		:= $(srctree)
 obj		:= $(objtree)