[PATCH v2] perf: fix building error in x86_64

[He Kuang <hekuang@huawei.com>]

When build with ARCH=x86_64, perf failed to compile with following error:

tests/builtin-test.o:(.data+0x158): undefined reference to `test__perf_time_to_tsc'
collect2: error: ld returned 1 exit status
Makefile.perf:632: recipe for target 'perf' failed
...

Which is caused commit c6e5e9fbc3ea1 ("perf tools: Fix building error
in x86_64 when dwarf unwind is on"), ARCH test in Makefile.perf
conflicts with tests/builtin-test.c's __x86_64__.
To x86/x86_64 platform, ARCH should always override to x86 while
IS_64_BIT stands for the actual architecture.

Signed-off-by: He Kuang <hekuang@huawei.com>
---
 tools/perf/config/Makefile.arch | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/tools/perf/config/Makefile.arch b/tools/perf/config/Makefile.arch
index ff95a68..836ba44 100644
--- a/tools/perf/config/Makefile.arch
+++ b/tools/perf/config/Makefile.arch
@@ -29,3 +29,7 @@ ifeq ($(LP64), 1)
 else
   IS_64_BIT := 0
 endif
+
+ifeq ($(ARCH), x86_64)
+  override ARCH := x86
+endif
-- 
2.2.0.33.gc18b867