perf tools: Fix building error in x86_64 when dwarf unwind is on

When build with 'make ARCH=x86' and dwarf unwind is on, there is a
compiling error:

   CC       /home/wn/perf/arch/x86/util/unwind-libdw.o
   CC       /home/wn/perf/arch/x86/tests/regs_load.o
 arch/x86/tests/regs_load.S: Assembler messages:
 arch/x86/tests/regs_load.S:65: Error: operand type mismatch for `push'
 arch/x86/tests/regs_load.S:72: Error: operand type mismatch for `pop'
 make[1]: *** [/home/wn/perf/arch/x86/tests/regs_load.o] Error 1
 make[1]: INTERNAL: Exiting with 25 jobserver tokens available; should be 24!
 make: *** [all] Error 2
 ...

Which is caused by incorrectly undefine macro HAVE_ARCH_X86_64_SUPPORT.
'config/Makefile.arch' tests __x86_64__ only when 'ARCH=x86_64'.
However, when building x86_64 kernel, ARCH=x86 is valid and commonly
used. Build systems, such as yocto, uses x86_64 compiler with 'ARCH=x86'
to build x86_64 perf, which causes mismatching.

As __LP64__ is defined for x86_64 as well, we can consolidate the
__x86_64__ check to the __LP64__ check and get rid of the IS_X86_64
IMHO.

(This patch is made by Namhyung Kim when replying my v1 patch:

https://lkml.org/lkml/2015/1/7/17

I modified the code to remove dependency on RAW_ARCH:

https://lkml.org/lkml/2015/1/7/865



Namhyung Kim didn't provide his SOB in his original email. I add
mine only for my modification.)

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Wang Nan <wangnan0@huawei.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/r/1421029255-23039-1-git-send-email-wangnan0@huawei.com


[ Namhyung provided his S-o-B on a followup to this patch thread on lkml ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>