perf test: Enhance the LLVM tests: add kbuild test

This patch adds a kbuild testcase to check whether kernel headers can be
correctly found.

For example:
  # mv /lib/modules/4.3.0-rc5{,.bak}
  # perf test LLVM

    38: Test LLVM searching and compiling                        : Skip

  # perf test -v LLVM
  ...
  <stdin>:11:10: fatal error: 'uapi/linux/fs.h' file not found
  #include <uapi/linux/fs.h>
          ^
  1 error generated.
  ERROR:	unable to compile -
  Hint:	Check error message shown above.
  Hint:	You can also pre-compile it into .o using:
     		 clang -target bpf -O2 -c -
	 with proper -I and -D options.
  Failed to compile test case: 'Test kbuild searching'
  test child finished with -2

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1446817783-86722-7-git-send-email-wangnan0@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/llvm.h

@@ -5,9 +5,11 @@
 #include <stdbool.h> /* for bool */
 
 extern const char test_llvm__bpf_base_prog[];
+extern const char test_llvm__bpf_test_kbuild_prog[];
 
 enum test_llvm__testcase {
 	LLVM_TESTCASE_BASE,
+	LLVM_TESTCASE_KBUILD,
 	__LLVM_TESTCASE_MAX,
 };