[PATCH] Documentation: insert an additional information to android.txt

[Joonsoo Kim <js1304@gmail.com>]

Without defining ARCH=arm, building a perf for Android ARM will be failed,
because it needs architecture specific files.
So add related information to a document.

Signed-off-by: Joonsoo Kim <js1304@gmail.com>

Cc: Irina Tirdea <irina.tirdea@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Steven Rostedt <rostedt@goodmis.org>

---
It is based on git://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git,
perf-core-for-mingo branch.

diff --git a/tools/perf/Documentation/android.txt b/tools/perf/Documentation/android.txt
index a39dbbb..8484c3a 100644
--- a/tools/perf/Documentation/android.txt
+++ b/tools/perf/Documentation/android.txt
@@ -48,7 +48,10 @@ For x86:
 II. Compile perf for Android
 ------------------------------------------------
 You need to run make with the NDK toolchain and sysroot defined above:
-  make CROSS_COMPILE=${NDK_TOOLCHAIN} CFLAGS="--sysroot=${NDK_SYSROOT}"
+For arm:
+  make ARCH=arm CROSS_COMPILE=${NDK_TOOLCHAIN} CFLAGS="--sysroot=${NDK_SYSROOT}"
+For x86:
+  make ARCH=x86 CROSS_COMPILE=${NDK_TOOLCHAIN} CFLAGS="--sysroot=${NDK_SYSROOT}"
 
 III. Install perf
 -----------------------------------------------
-- 
1.7.9.5