tools include: define READ_ONCE/WRITE_ONCE for C++

[Sandipan Das]

From: Li Zhijian <lizhijian@xxxxxxxxxxxxxx>

since 6aa7de0, we failed to build perf with C++(clang)
to fix the following compile errors
--------------
lizhijian@haswell-OptiPlex-9020:~/lkp/linux/tools/perf$ make LLVM_CONFIG=/usr/bin/llvm-config-3.9 LIBCLANGLLVM=1
...
  CC       util/probe-finder.o
In file included from /home/lizj/linux/tools/perf/util/util.h:13:0,
                 from /home/lizj/linux/tools/perf/util/util-cxx.h:20,
                 from util/c++/clang-c.h:5,
                 from util/c++/clang-test.cpp:2:
/home/lizj/linux/tools/include/asm/../../arch/x86/include/asm/atomic.h: In function âint atomic_read(const atomic_t*)â:
/home/lizj/linux/tools/include/linux/compiler.h:157:45: error: use of deleted function âatomic_read(const atomic_t*)::<anonymous union>::<constructor>()â
  ({ union { typeof(x) __val; char __c[1]; } __u; __read_once_size(&(x), __u.__c, sizeof(x)); __u.__val; })
                                             ^
/home/lizj/linux/tools/include/asm/../../arch/x86/include/asm/atomic.h:28:9: note: in expansion of macro âREAD_ONCEâ
  return READ_ONCE((v)->counter);
         ^
/home/lizj/linux/tools/include/linux/compiler.h:157:11: note: âatomic_read(const atomic_t*)::<anonymous union>::<constructor>()â is implicitly deleted because the default definition would be ill-formed:
  ({ union { typeof(x) __val; char __c[1]; } __u; __read_once_size(&(x), __u.__c, sizeof(x)); __u.__val; })
           ^
/home/lizj/linux/tools/include/asm/../../arch/x86/include/asm/atomic.h:28:9: note: in expansion of macro âREAD_ONCEâ
  return READ_ONCE((v)->counter);
         ^
/home/lizj/linux/tools/include/linux/compiler.h:157:11: error: uninitialized const member in âunion atomic_read(const atomic_t*)::<anonymous>â
  ({ union { typeof(x) __val; char __c[1]; } __u; __read_once_size(&(x), __u.__c, sizeof(x)); __u.__val; })
           ^
/home/lizj/linux/tools/include/asm/../../arch/x86/include/asm/atomic.h:28:9: note: in expansion of macro âREAD_ONCEâ
  return READ_ONCE((v)->counter);
         ^
/home/lizj/linux/tools/include/linux/compiler.h:157:23: note: âconst int atomic_read(const atomic_t*)::<anonymous union>::__valâ should be initialized
  ({ union { typeof(x) __val; char __c[1]; } __u; __read_once_size(&(x), __u.__c, sizeof(x)); __u.__val; })
                       ^
/home/lizj/linux/tools/include/asm/../../arch/x86/include/asm/atomic.h:28:9: note: in expansion of macro âREAD_ONCEâ
  return READ_ONCE((v)->counter);
         ^
  LD       tests/perf-in.o
...
--------------

Signed-off-by: Li Zhijian <lizhijian@xxxxxxxxxxxxxx>
---
 tools/include/linux/compiler.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/tools/include/linux/compiler.h b/tools/include/linux/compiler.h
index 07fd03c..e4c8a0d 100644
--- a/tools/include/linux/compiler.h
+++ b/tools/include/linux/compiler.h
@@ -86,6 +86,10 @@
 
 #define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x))
 
+#ifdef __cplusplus
+#define READ_ONCE(x) ACCESS_ONCE(x)
+#define WRITE_ONCE(x, val) ACCESS_ONCE(x) = val
+#else
 #include <linux/types.h>
 
 /*
@@ -160,6 +164,7 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
 #define WRITE_ONCE(x, val) \
 	({ union { typeof(x) __val; char __c[1]; } __u = { .__val = (val) }; __write_once_size(&(x), __u.__c, sizeof(x)); __u.__val; })
 
+#endif /* __cplusplus */
 
 #ifndef __fallthrough
 # define __fallthrough