perf tools: Makefile: Use gcc to determine ARCH

The original Makefile uses "uname -m" to determine ARCH.
This causes problem on x86 when compile perf tool on 32 bit
userspace with a 64 bit kernel.

 bench/../../../arch/x86/lib/memcpy_64.S: Assembler messages:
 bench/../../../arch/x86/lib/memcpy_64.S:28: Error: bad register name `%rdi'

This is because "uname -m" returns x86_64 and memcpy_64.S is
included in 32 bit build.
Reported-by: Riccardo Magliocchetti <riccardo.magliocchetti@gmail.com>
Signed-off-by: Lin Ming <ming.m.lin@intel.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
Link: http://lkml.kernel.org/r/1304743274.3132.17.camel@localhostSigned-off-by: Ingo Molnar <mingo@elte.hu>

tools/perf/Makefile

@@ -35,15 +35,21 @@ ARCH ?= $(shell echo $(uname_M) | sed -e s/i.86/i386/ -e s/sun4u/sparc64/ \
 				  -e s/ppc.*/powerpc/ -e s/mips.*/mips/ \
 				  -e s/sh[234].*/sh/ )
 
+CC = $(CROSS_COMPILE)gcc
+AR = $(CROSS_COMPILE)ar
+
 # Additional ARCH settings for x86
 ifeq ($(ARCH),i386)
         ARCH := x86
 endif
 ifeq ($(ARCH),x86_64)
-	RAW_ARCH := x86_64
 	ARCH := x86
+	IS_X86_64 := $(shell echo __x86_64__ | ${CC} -E -xc - | tail -n 1)
+	ifeq (${IS_X86_64}, 1)
+		RAW_ARCH := x86_64
 		ARCH_CFLAGS := -DARCH_X86_64
 		ARCH_INCLUDE = ../../arch/x86/lib/memcpy_64.S
+	endif
 endif
 
 #
@@ -119,8 +125,6 @@ lib = lib
 
 export prefix bindir sharedir sysconfdir
 
-CC = $(CROSS_COMPILE)gcc
-AR = $(CROSS_COMPILE)ar
 RM = rm -f
 MKDIR = mkdir
 FIND = find