perf scripting perl: Force to use stdbool

When building perf for arm64 I hit a warning (and be treated as an
error) like below:

 aarch64-oe-linux-gcc -o .../scripts/perl/Perf-Trace-Util/Context.o -c -Wbad-function-cast \
         ... scripts/perl/Perf-Trace-Util/Context.c

 In file included from .../usr/lib64/perl/5.14.3/CORE/perl.h:2464:0,
                  from Context.xs:23:
 /.../usr/lib64/perl/5.14.3/CORE/handy.h:108:0: error: "bool" redefined [-Werror]
  #  define bool char
  ^
 In file included from /.../usr/src/kernel/tools/include/linux/types.h:4:0,
                  from /.../usr/src/kernel/arch/arm64/include/uapi/asm/sigcontext.h:19,
		  from /.../usr/include/bits/sigcontext.h:27,
		  from /.../usr/include/signal.h:340,
		  from /.../usr/include/sys/param.h:28,
		  from /.../usr/lib64/perl/5.14.3/CORE/perl.h:678,
		  from Context.xs:23:
  /.../usr/lib/aarch64-oe-linux/gcc/aarch64-oe-linux/4.9.2/include/stdbool.h:33:0: note: this is the location of the previous definition
    #define bool _Bool

Looks like the failure is caused by arm64 uapi/asm/sigcontext.h, which
includes linux/types.h while other archs not.

Current perl consider this problem:

http://perl5.git.perl.org/perl.git/commit/bd31be4baa3ee68abdb92c0db3200efe0fad903b

However there are users which use old version of perl.

This patch includes stdbool.h before Context.xs and define HAS_BOOL to
prevent perl'e headers define its own 'bool'. Code is learn from perl's
git tree.
Signed-off-by: Wang Nan <wangnan0@huawei.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Li Zefan <lizefan@huawei.com>
Link: http://lkml.kernel.org/r/1421671397-4659-1-git-send-email-wangnan0@huawei.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/scripts/perl/Perf-Trace-Util/Context.c

@@ -5,7 +5,10 @@
  *	ANY CHANGES MADE HERE WILL BE LOST! 
  *
  */
-
+#include <stdbool.h>
+#ifndef HAS_BOOL
+# define HAS_BOOL 1
+#endif
 #line 1 "Context.xs"
 /*
  * Context.xs.  XS interfaces for perf script.